Around a pentium II 300.

A) depends on workload, K6-2+ is a very different beast to Intel's CPUs of the time.

K6-2+ had 3DNow, which was very, very fast in the very few things that supported it. It had a typically weak FPU (at least when compared to the P6 monster), and again compared to P6 was slightly stronger in 16b code and weaker in 32b code.

So:
- if your game actually uses 3DNow, it will run better on K6-2+ than a similarly clocked P2.
- if you're running FPU-heavy stuff (Quake...), a P2 will get 50% higher performance at the same clock, i.e. perform equivalently to a 50% higher clocked K6-2+. So at best you CPU will be comparable to a P2-300.
- if you're running ALU-heavy 32b stuff (most other mid 1990s games), the difference will be at most 10%, so comparable to a P2-400 at least.
- if you're running ALU 16b stuff (i.e. DOS games), the K6-2+ can beat a P2 clock-for-clock - but will suffer from slower bus speed, but parity with P2-450 would be possible in Doom, I suspect.

You say your overclocked AGP port is the issue stopping you running at 83MHz. Maybe it's worth trying some different AGP cards. I had it running at 83MHz with AGP. Alternative is to go PCI, as with the ancient AGP implementation on the SiS 5591 it's not really giving you significantly more performance.

B) generally the best voltage to set is the lowest that leaves the system fully stable. The K6-2+ CPUs were intended as laptop parts and designed for low power. You should be able to get away with a significant undervolt at this level of underclocking, but just one way to find out with your CPU: try it, stress it and if it's stable, keep it.

You should run it at its recommended voltage.
There is no need to increase the voltage for over clocking.
You can use a utility called “Setmul” ( set multiplier ) to down clock the CPU.
You can also disable motherboard cache and cpu cache to down clock it in bios.

https://www.philscomputerlab.com/k6-2-2-3-resources.html

I have tested the functionality of Voodoo3 2000 PCI even at FSB 83MHz on almost the same board (M590). But it doesn't have an AGP port, so I can't test the AGP cards. The integrated one (SiS 6326 AGP 2x) works on FSB 83MHz without any problems either. You have a more powerful and faster CPU, but even on an ordinary K6-2 300@400/380 (66x6 or 83x4.5) the shift in memory throughput is noticeable. Even in 3DM99 the CPU Mark is higher in the slower 380@83 than 400@66 - the score of the graphics card is at the limit of its performance, therefore it does not change.

Fastest K6-III+ 550 MHz is equivalent of Pentium II 300-350 MHz in most of games. Performance of K6-2+ 450 MHz @75 MHz FSB with good motherboard should be maybe around Pentium II 233 😀

LubieCipy wrote on 2021-10-13, 18:21:

Fastest K6-III+ 550 MHz is equivalent of Pentium II 300-350 MHz in most of games. Performance of K6-2+ 450 MHz @75 MHz FSB with good motherboard should be maybe around Pentium II 233 😀

Only if by "most games" you mean (Gl)Quake:

Most games that run on these PCs don't even use FPU, so there's little advantage to P2, and some (Quake2) even use 3DNow, which makes a big difference:

And as for 16 bit code...

Ydee wrote on 2021-10-13, 08:27:

You have a more powerful and faster CPU, but even on an ordinary K6-2 300@400/380 (66x6 or 83x4.5) the shift in memory throughput is noticeable.

K6-2+ has an integrated 128KB L2 cache running at full CPU speed which makes a difference over the regular K6-2.

dionb wrote on 2021-10-13, 20:57:

Most games that run on these PCs don't even use FPU, so there's little advantage to P2, and some (Quake2) even use 3DNow, which makes a big difference:

This is correct but there are also video card drivers that could use 3DNow! instructions (mainly nVidia and 3Dfx) or the FPU.

And as for 16 bit code...

The reason why P6 based CPUs has such mediocre 16-bit performance was due to partial register stalling, it was much worse with Pentium Pro CPUs.

I GOT IT RUNNING AT 500MHz, 83MHz FSB.

I changed the agp card to a 3D Labs Permidia 2. That's all I did, and it's taking 83 like a champ. I don't know if they made the dies for those chips out of adamantium or what, but this is the first time I've ever seen an AGP card run at 83.

I'm switching this build to primarily use software rendering until I can afford a Voodoo 2 2000 PCI or similar, but for now this seems to work well.

If it fries the AGP card, I'll just buy a real cheap ATI Rage XL 8MB PCI online. They're like $15 USD.

Don't forget to enable write combining for that K6-2+ CPU. 😉 It will boost the performance on VESA resolutions such as 640x480.

Enabling write combining is something I know nothing about, but I'd definitely be interested in learning.

Quick question, would this BIOS update I applied to use the K6-2+ work, or is it something I need to change via software?

http://web.inter.nl.net/hcc/J.Steunebrink/k6plus.htm

athlon_p0wer wrote on 2021-10-14, 20:13:

Enabling write combining is something I know nothing about, but I'd definitely be interested in learning.

You can learn from Phil from the following YouTube video: https://www.youtube.com/watch?v=D_QTIadLd1w. This also works for the K6-2+, however there is an even better utility for that called K6INIT.

Quick question, would this BIOS update I applied to use the K6-2+ work, or is it something I need to change via software?

The unofficial BIOS update from Jan would properly fix the CPU identification on POST and enable write allocation automatically. If the BIOS lacks support for that CPU it would be identified as a 486DX2-66 (at least in my case) assuming that it the computer performed POST successfully, but write allocate (and other features) can be enabled via software.

Also make sure that you disable both Video and System BIOS cacheable for better stability with the K6-2+.

dionb wrote on 2021-10-13, 20:57:

LubieCipy wrote on 2021-10-13, 18:21:

Fastest K6-III+ 550 MHz is equivalent of Pentium II 300-350 MHz in most of games. Performance of K6-2+ 450 MHz @75 MHz FSB with good motherboard should be maybe around Pentium II 233 😀

Only if by "most games" you mean (Gl)Quake:

Nope, I mean most games.

Pentium II/III VS K6-III+

P2/P3 VS K6-3+ - A Great Battle Commences

LubieCipy wrote on 2021-10-14, 22:40:

Nope, I mean most games. […]
Show full quote

dionb wrote on 2021-10-13, 20:57:

LubieCipy wrote on 2021-10-13, 18:21:

Fastest K6-III+ 550 MHz is equivalent of Pentium II 300-350 MHz in most of games. Performance of K6-2+ 450 MHz @75 MHz FSB with good motherboard should be maybe around Pentium II 233 😀

Only if by "most games" you mean (Gl)Quake:

Nope, I mean most games.

Pentium II/III VS K6-III+

P2/P3 VS K6-3+ - A Great Battle Commences

Only if by "most games" you mean Win32 3D games. Your references do not contain even a single 16-bit/DOS (or even Win32 2D ) title.
BTW Dionb has given a detailed and differentiated description about the performance characteristics of K6 -2/3.
(K6-2+ Questions)
Your much more simplistic answer has not added any more useful info to that.

Falcosoft wrote on 2021-10-15, 04:21:

Only if by "most games" you mean Win32 3D games. Your references do not contain even a single 16-bit/DOS (or even Win32 2D ) tit […]
Show full quote

LubieCipy wrote on 2021-10-14, 22:40:

Nope, I mean most games. […]
Show full quote

dionb wrote on 2021-10-13, 20:57:

Only if by "most games" you mean (Gl)Quake:

Nope, I mean most games.

Pentium II/III VS K6-III+

P2/P3 VS K6-3+ - A Great Battle Commences

Only if by "most games" you mean Win32 3D games. Your references do not contain even a single 16-bit/DOS (or even Win32 2D ) title.
BTW Dionb has given a detailed and differentiated description about the performance characteristics of K6 -2/3.
(K6-2+ Questions)
Your much more simplistic answer has not added any more useful info to that.

2d games in general do not require the maximum amount of horsepower a K62 or a P6 could go, nor require 3d accelrators. In a lot of cases the main reason somone picks a socket 7 platform is its it's ability to go slow and have nothing to do with it's ability to go fast. Becasue if you want to go fast it's not the platform for doing so. so I do not see how a speed comparison for example a P6 and a K62 at playing wolfenstien 3d, its silly. A hotrodded 486 can play DOOM at a playable framerate, and a 586 can play it at an enjoyible framrate. So I do not personnnaly see any value in seeing 2d benchmarks of K62s and P6s becasue any 2d game you throw at one will be overkill. Which is obvious.

Warlord wrote on 2021-10-15, 04:57:

Falcosoft wrote on 2021-10-15, 04:21:

Only if by "most games" you mean Win32 3D games. Your references do not contain even a single 16-bit/DOS (or even Win32 2D ) tit […]
Show full quote

LubieCipy wrote on 2021-10-14, 22:40:

Nope, I mean most games.

Pentium II/III VS K6-III+

P2/P3 VS K6-3+ - A Great Battle Commences

Only if by "most games" you mean Win32 3D games. Your references do not contain even a single 16-bit/DOS (or even Win32 2D ) title.
BTW Dionb has given a detailed and differentiated description about the performance characteristics of K6 -2/3.
(K6-2+ Questions)
Your much more simplistic answer has not added any more useful info to that.

2d games in general do not require the maximum amount of horsepower a K62 or a P6 could go, nor require 3d accelrators. In a lot of cases the main reason somone picks a socket 7 platform is its it's ability to go slow and have nothing to do with it's ability to go fast. Becasue if you want to go fast it's not the platform for doing so. so I do not see how a speed comparison for example a P6 and a K62 at playing wolfenstien 3d, its silly. A hotrodded 486 can play DOOM at a playable framerate, and a 586 can play it at an enjoyible framrate. So I do not personnnaly see any value in seeing 2d benchmarks of K62s and P6s becasue any 2d game you throw at one will be overkill. Which is obvious.

Have you ever tried playing e.g. Build engine games at higher resolutions ? Try Duke Nukem 3D, Blood, Redneck Rampage etc. above 640x480 to get not so overkill results...

Not exactly on topic, but my two cents on the performance debate: the K6-2/3(+) was decent for games up to 1999 (maybe some from 2000 as well). Now, when I say decent, I'm referring to the "playable" standard of the time. Me and most people I knew were perfectly content with 20+ FPS (30 FPS would've been phenomenal). So, taking that into account, the K6-2 (and especially the K6-3 or K6-2/3+) would've been fine for most people.

So it all comes down to what exactly one is looking for. If you just want to relive the experience you had back in the day and are not looking for modern "playability" standards, then the K6-2/3 family is fine and the platform is flexible and (to me, at least) very exciting - you usually need to fiddle around a lot with it to achieve the optimum level of performance and stability.
If, however you just want to play most or all the games from that era at 100 or even 200+ FPS, then, truthfully, you are better off with an Athlon XP Thoroughbred/Barton on a VIA KT600 motherboard - hands down one of the most flexible platforms in my book: extremely fast for all Windows 98 games and if you add a Yamaha YMF7x4 sound card, 99% of DOS games will also work (and sound) just fine.

AGP at 83MHz is cool, you'll get "AGP 2,5" performance as the bandwidth increases as well!

If you've got them, you could cherry pick to see if there's an AGP card that takes the whole 100MHz AGP if you change too that. Most likely it'll be a Nvidia. I've got a GF4 MX440 that takes the 100MHz AGP (P3B-f, 440BX motherboard at 150fsb). That way your K6-2+ will be even happier! 😁

waterbeesje wrote on 2021-10-15, 08:19:

AGP at 83MHz is cool, you'll get "AGP 2,5" performance as the bandwidth increases as well!

If you've got them, you could cherry pick to see if there's an AGP card that takes the whole 100MHz AGP if you change too that. Most likely it'll be a Nvidia. I've got a GF4 MX440 that takes the 100MHz AGP (P3B-f, 440BX motherboard at 150fsb). That way your K6-2+ will be even happier! 😁

On SS7, the bottleneck is not the AGP interface, it's the CPU performance. 😀
In my experience, a GeForce 2 GTS is barely able to saturate an AGP 1X interface, a GeForce 3 (Ti 200/500) will work fine at AGP 2X. Even a GeForce 4 Ti runs comfortably @ AGP 2X in most scenarios.

Back to SS7, on most motherboards, you will actually want to stick to AGP 1X for the much improved stability.

athlon_p0wer wrote on 2021-10-14, 20:13:

Enabling write combining is something I know nothing about, but I'd definitely be interested in learning.

I can help you there as I've only just discovered tweaking that stuff myself. Here's the post where I explain what I've learned about it. In my case, the system I had definitely did not support the K6-II/-III series CPUs, nor the write combining and write allocation features out-of-box.