I thought lowest multiplier you can go with pentium II is 2x. At least I couldn't go below 133Mhz.

The common Pentium II 450MHz Slot 1 is multiplier locked as far as I know so it runs only at 450Mhz @ 4.5 x fsb100 or 300Mhz @ 4.5 x fsb66.
You can find details on unlocked and multiplier limited Pentiums in this thread:
Which Pentium IIs can be underclocked?

To me Coppermine/tualatin P3 is the best all around retro build hands down, so it's my vote. Everybody always mentions the speed sensitive games but are you really going to spend THAT much time on them? It's up to you to decide how critical they are, and that can be a rabbit hole. Also I believe those games would run perfectly fine in DOSBox on the P3 itself in a pinch. 800mhz coppermine will run half-life nicely and can go into year 2000 games like Diablo II. If it's critically important to get games like wing commander running perfectly while still having the ability to play later 9x titles, maybe consider a s7/ss7 build instead. If you need EVERYTHING to run perfectly, you'll have to get quite a few computers 😜

Also I don't believe Jazz Jackrabbit is speed sensitive (as mentioned by OP). It's been a number of years since I've played that but as far as I know it was just compiled with an old version of Turbo Pascal that breaks at 200mhz, run a readily available patching tool (tppatch.exe??) and it will run perfectly fine on machines above 200mhz.

Quick search brings this up: https://www.jazz2online.com/downloads/341/jazz-1-tppatch/
Try running that in your jazz directory and running it on your faster system.

Why not get a 1GHz + 100 MHz Slot 1 Pentium-III such as http://www.cpu-world.com/sspec/SL/SL4BR.html? Given the Voodoo 4 is quite uncommon then an uncommon CPU would seem appropriate

The P!!! - 1 GHz would possibly also run at 66 and 100 MHz FSB, giving you 500 and 750 MHz respectively. At these speeds your AGP will also be inside specs.

On the other hand, the PII would also run at 66 MHz FSB, thus 300 MHz.

As written by others, I would think the Mendocino core is multiplier locked - only the first few production weeks, they were limited, rather than locked, IIRC.

Aside from being anal about period correctness there is absolutely no point in going with a slow P2 rather than a fast P3.

appiah4 wrote:

Aside from being anal about period correctness.

I would argue that a P-III is period correct as it was quite common for swap out P-II CPUs for P-III CPUs.

I did this myself on my Gigabyte GA-6BXD system, I started with 2 x P-II 450 and when they came out upgraded to a pair of 1GHz (100MHz FSB) P-III slot 1 CPUs which my system still has.

H3nrik V! wrote:

As written by others, I would think the Mendocino core is multiplier locked - only the first few production weeks, they were limited, rather than locked, IIRC.

You must have meant deschutes, because Mendocino is the celeron's core 😁 (and they've all been locked entirely). If I understand properly, the earliest deschutes are totally unlocked, later they were limited and finally they were locked. They may be some limited p2 450 out there, but they must be pretty rare.

Deksor wrote:

H3nrik V! wrote:

As written by others, I would think the Mendocino core is multiplier locked - only the first few production weeks, they were limited, rather than locked, IIRC.

You must have meant deschutes, because Mendocino is the celeron's core 😁 (and they've all been locked entirely). If I understand properly, the earliest deschutes are totally unlocked, later they were limited and finally they were locked. They may be some limited p2 450 out there, but they must be pretty rare.

Yeah, you're right, I ment Deschutes .. Mendocino didn't sound right either, but I was only on my third or fourth mug of coffee today, so anything might have sounded wrong 🤣

Thanks for all replies! Indeed, as many have pointed out, the Pentium II multiplier is locked to 4, so the lowest it can go is 266MHz - it is a 400MHz model, not 450MHz as I had previously stated.

I was able to apply the Jazz Jackrabbit patch and that solved the speed issue (I remember reading about that patch before but it was a long time ago and I forgot, thanks for the folks who raised this up); Alone in the Dark seemed just as hard to trigger the run on the 266MHz Pentium III as it did on the Pentium III 1GHz.

I'll go with the Pentium III- the only real pro for using the Pentium II didn't turn out as I expected, so really makes no sense on having it on my main build. Maybe later in the future when I have room to have multiple builds....

bregolin wrote:

Thanks for all replies! Indeed, as many have pointed out, the Pentium II multiplier is locked to 4, so the lowest it can go is 266MHz - it is a 400MHz model, not 450MHz as I had previously stated.

I was able to apply the Jazz Jackrabbit patch and that solved the speed issue (I remember reading about that patch before but it was a long time ago and I forgot, thanks for the folks who raised this up); Alone in the Dark seemed just as hard to trigger the run on the 266MHz Pentium III as it did on the Pentium III 1GHz.

I'll go with the Pentium III- the only real pro for using the Pentium III didn't turn out as I expected, so really makes no sense on having it on my main build. Maybe later in the future when I have room to have multiple builds....

I have a pentium II 300Mhz cpu that can go down to 2x66Mhz with asus P2B motherboard. There must be some kind of differences between P2 cpus.

Baoran wrote:

bregolin wrote:

Thanks for all replies! Indeed, as many have pointed out, the Pentium II multiplier is locked to 4, so the lowest it can go is 266MHz - it is a 400MHz model, not 450MHz as I had previously stated.

I was able to apply the Jazz Jackrabbit patch and that solved the speed issue (I remember reading about that patch before but it was a long time ago and I forgot, thanks for the folks who raised this up); Alone in the Dark seemed just as hard to trigger the run on the 266MHz Pentium III as it did on the Pentium III 1GHz.

I'll go with the Pentium III- the only real pro for using the Pentium III didn't turn out as I expected, so really makes no sense on having it on my main build. Maybe later in the future when I have room to have multiple builds....

I have a pentium II 300Mhz cpu that can go down to 2x66Mhz with asus P2B motherboard. There must be some kind of differences between P2 cpus.

You probably have an early production Klamath CPU that is multiplier unlocked. Hold onto it.

appiah4 wrote:

Baoran wrote:

bregolin wrote:

Thanks for all replies! Indeed, as many have pointed out, the Pentium II multiplier is locked to 4, so the lowest it can go is 266MHz - it is a 400MHz model, not 450MHz as I had previously stated.

I was able to apply the Jazz Jackrabbit patch and that solved the speed issue (I remember reading about that patch before but it was a long time ago and I forgot, thanks for the folks who raised this up); Alone in the Dark seemed just as hard to trigger the run on the 266MHz Pentium III as it did on the Pentium III 1GHz.

I'll go with the Pentium III- the only real pro for using the Pentium III didn't turn out as I expected, so really makes no sense on having it on my main build. Maybe later in the future when I have room to have multiple builds....

I have a pentium II 300Mhz cpu that can go down to 2x66Mhz with asus P2B motherboard. There must be some kind of differences between P2 cpus.

You probably have an early production Klamath CPU that is multiplier unlocked. Hold onto it.

But is there any speed sensitive game that doesn't work at 300Mhz but starts working if you slow it down to 133Mhz? Basically I am asking if there is any practical advantage for being able to slow down the cpu when it comes to P2 CPUs?

Yes, for titles programmed in Turbo Pascal, but that bug can be patched.

There are DOS games that go bonkers when the CPU is clocked beyond (or is it at?) 200MHz.

bregolin wrote:

- 133 FSB - it's a bit of a hack on the i440BX chipset, and on this Asus board, it also overclocks the AGP interface to 2/3 of the FSB, something that could cause instability

The i440BX chipset on the Asus board has no problems with 133MHz, but you might want to check first whether your expensive Voodoo card likes almost 89MHz FSB. NVIDIA Riva TNT2 and more recent work fine with it. https://www.anandtech.com/show/574

SpectriaForce wrote:

The i440BX chipset on the Asus board has no problems with 133MHz, but you might want to check first whether your expensive Voodoo card likes almost 89MHz FSB. NVIDIA Riva TNT2 and more recent work fine with it. https://www.anandtech.com/show/574

That was an excellent article, thanks for sharing it! AnandTech and Tom's Hardware were all I needed back in the day...

Yep, I had been running the 440BX at 133 FSB with no issues, but it looks like my Voodoo 4 is about to give up; video memory tests shows memory errors and it would eventually lock up with 133 FSB when playing games. These memory errors are also present with 100 or 66 FSB, but at 100 FSB it seems much more stable as I played many games for a long period of time with no crashes. It is being properly cooled and it has never been overclocked before, so I guess it's just dying of old age. Sad.

appiah4 wrote:

There are DOS games that go bonkers when the CPU is clocked beyond (or is it at?) 200MHz.

Is it about clock speed or actual speed of the cpu though?
I don't know how 133Mhz 486, 133Mhz Pentium and 133Mhz Pentium II cpus compare to each other when it comes to actual cpu speeds though? IPC are different, but not sure how much.

Baoran wrote:

appiah4 wrote:

There are DOS games that go bonkers when the CPU is clocked beyond (or is it at?) 200MHz.

Is it about clock speed or actual speed of the cpu though?
I don't know how 133Mhz 486, 133Mhz Pentium and 133Mhz Pentium II cpus compare to each other when it comes to actual cpu speeds though? IPC are different, but not sure how much.

It's specifically about the clockspeed.