It really depends what you want to do with them. I for one am a greedy bastard and I like to play everything in as high detail and on silly resolutions - as such, I tend to go slightly over-spec with my builds. Here are some of my machines and their purpose:

Main retro rig: AMD K6-III @ 550Mhz / Aopen AX59PRO (VIA MVP3 ATX) / Riva TNT2 PRO / 2x Voodoo 2 8MB SLi / Yamaha YMF744 / Primax Soundstorm M16C (GUS GF1 clone)
- I use this machine for most of my retro needs. The CPU can be clocked up to 600Mhz and as low as 200Mhz while disabling all cache using a utility called SetMUL. This lets me play speed sensitive games in DOS. At 200Mhz with all cache off, it's about as slow as a 33Mhz 386.
- The Yamaha card is used for Windows games as well as older 3dfx DOS titles with MIDI music, like Descent 2. It has an excellent MIDI driver closely emulating a Yamaha SW60 synth. As such I run as many games under windows as I can - and most DOS games that support General MIDI work well in a Win98 DOSBOX.
- The Gravis card I use in pure DOS. Since it's not PnP, it doesn't push it'self on the windows environment allowing for the proper operation of the Yamaha card. In dos however, the Yamaha does not have a General MIDI TSR, forcing me to use the GUS. It's great for late DOS games, especially ones that have native GUS support.
- I mainly play stuff like Red Alert, C&C95, Dungeon Keeper, Descent 2 (with 3dfx patch), Carmageddon (3dfx patch), Duke Nukem 3D, Nuclear Strike, GL-Quake, Quake2, Hexen II, Expandable, Populous 3, SHOGO, Mechwarrior 3, Pandemonium, and others elusively on this machine.

Secondary retro rig: AMD Athlon XP 3200+ 2333Mhz (166x14) / Abit AN7 (nForce 2 Ultra) / 1GB DDR400 / Soltek FX5900 XT / Sound Blaster LIVE!
- This machine dual boots win98 and XP. XP is mainly for maintenance, networking and internet access since not all my favorite games run well on XP but do so on 98. I also use it to put stuff I get off the net on floppy drives for old machines with no network access. This machine is fast enough to run all my games at 1280x1024 with some AA.
- I run Quake 3 Arena, Unreal Tournament 99 and 2003, Dungeon Keeper 2, Black and White, Descent 3, Descent Freespace, Mechwarrior 4, Legacy of Kain Soul Reaver 1, 2 and Defiance, Sacrifice, Unreal 2 and many others exclusively on this build.

I have a couple of 486 (586) builds, but they're more of a niche since they're too slow for some games and too fast for others. One houses my Yamaha SW20-PC since it won't run on faster computers, but I'm planning to move it to a Pentium 1 build. I use that 486 for sierra games (King's Quest, Space Quest, Gobliins, etc) since they all support general midi and the SW20 sounds best out of all GM midi cards / modules I own. The 386 and 286 machines in my signature are for speed sensitive games. The 286 can run XT games very well.

As for your machines, you really didn't post too many details. If you want good MIDI for older games, you need a GM Compatible card, a GUS or a Roland MT32. These work fine in a 486/pentium 1. If you want to run early 3D games I recommend getting a 3DFX card - a Voodoo 2, 3 or Banshee since quite a few early 3D games were Glide-only (3dfx Carmageddon, 3dfx Descent, GL-Qake and so on). If you just want to run old games and are not particullar about MIDI, 3D or quality / speed, turn the 486 into a DOS machine and the Athlon XP or socket 478 machine in a windows 98 rig.

The 486 is useful for older DOS speed-sensitive games IF it has a working TURBO function. If you get a Roland MT32 or a General Midi compatible ISA card, lots of old games have awsome MIDI music. I personally didn't know how good MIDI could sound until a year ago when I first tested my Yamaha SW20, and I was blown away. I didn't even know MIDI could sound so good since I couldn't afford a general midi card back in the day.

The pentium 1 would be a good starting point for a Glide rig. Upgrade the CPU as much as it will go (Pentium 200 or 233MMX) and throw a Voodoo 2 in there. If you like old Glide games, this build is a start.

As for the Athlon / P4 - see witch one is the fastest, get a fast AGP video card with win98 drivers and build an extreme win98 rig.

The rest have no use as retro gaming rigs in my view.

Oh yes, C&C 😁
Actually got hold of the C&C first decade, but since that's WinXP, I might have a fair chance of it running ok / compatibility on my main rig.

Only ever had 1 Glide game ... Archimedian Dynasty

Rig 1, currently has GT730 and Realtek HD audio

The two P4 640, video card currently my old HD5670, as their old cards have dying fans and wouldn't even LOAD Win10, sound - CMI9880 (forced to use last XP driver)

The other scrapper I picked up, graphics are extreme 2, sound probably Intel AC97 - still itching to turn it into a Core 2 build, if I get a cheap LGA775 board that uses DDR3, I've got 4GB spare, and got my eye on some really cheap C2Ds - going for peanuts compared to quads.

Athlon XP - friend's old machine, has Geforce 2MX, 256MB SDRAM (I think I have a spare 512MB to add)

Athlon Tbird = my own old Win98SE with bad case of Windows rot - has Gefore 4MX (tempted to give this card to the Athlon XP, as it's fundamentally a full Geforce 2. has SB Live. Has 384MB RAM and is VERY fussy, only takes 128's or low density 256. 3.3V AGP.

P75 - gift, has onboard S3 trio, 32MB RAM (can take more, but cannot cache it), think it's only S5 not S7

Other spares...
PCI SB 128
ISA SB16 ASP multi CD with midi db attached (I'm sure that has it's uses for a good DOS machine!)
Another Geforce 2MX (used but boxed Creative)
3.3V AGP Rage 128
PCI S3 Savage 4
Another SB16 (I think)

Tested the S478 P4 - not impressed, the Intel Extreme 2 graphics date back to when onboard were a bad joke, I think it could face gutting for a Core 2 build, but got some IDE drives and PCI stuff to test, so it may serve as a test victim for a while.

The threshold of a Linux build, other than for text mode or a very light front end, has definitely gone up.

The P75 is not MMX capable, big plus (and minus) is the small case with card riser, but it looks like coming up too fast for a DOS box and not enough for much else... high performance Win3 box?

Clean forgot my other relic, which IS a P200 MMX - with CL5446 PCI.

So the DX4-100 is the lowest performance out of all, and maybe possible to slug it... real DOS system.

Leaning toward a possible multiboot on the Athlon XP, can run Windows XP adequately, would also be compatible with 98. Then the 486 could do the pure DOS

Yeah, the DX4 would make a perfect DOS rig.

As for the P75, I would upgrade to P133 (if your board can handle it, otherwise P120) and make it a DOS/Win98SE rig for later DOS games.

Matth79 wrote:

Tested the S478 P4 - not impressed, the Intel Extreme 2 graphics date back to when onboard were a bad joke, I think it could face gutting for a Core 2 build, but got some IDE drives and PCI stuff to test, so it may serve as a test victim for a while.

From what I recall the Intel Extreme 2 "graphics" can best be described as a Geforce 2 gts or so w/o HW T&L. So in other words, if you do not have an AGP slot it is terrible. A Geforce 6200 makes it bearable however, but still not ideal. And that is depending on whether or not your motherboard supports a proper 800fsb P4 or not. And it will still suck TBH in comparison.

Socket 478 can be nice for a super fast Win98 PC which doesn't like muli core CPU's including P4's with Hyper threading. But that's about the only real use I can see for them.

I actually don't find my 486 that useful. Its right in the middle. By now most dos games no longer have speed issues on faster machines, and if anything a 486 is a bit slow, Duke3d, Quake, Red Alert are some examples.
and most speed sensitive games want something slower.

BUT it is my most loved PC and find reasons to play games on it, basically anything round 95 or earlier that isn't speed sensitive.