Another PIII build is underway. I've managed to accumulate some desirable retro hardware again -- first a Voodoo3 3000 AGP, then an Aureal Vortex 2, and now I've managed to land myself a microATX i815 board out of some IBM NetVista. Figuring out the pinout on that thing's front panel is going to be fun, but once I manage that, I should have a pretty decent platform for a late-90s Glide/A3D machine. Not going all out -- since it's just a Voodoo3 there's no point in going any faster than a PIII-1000EB, 512MB of RAM (the chipset's cap and also the reasonable limit for 9x, though with a patch you can use more) and a 120GB SSD on a SATA to IDE converter.
9x has no concept of TRIM and through IDE it wouldn't work anyway -- even on what seems like native SATA on my i865 board XP can't use any tools to force TRIM on its SSD, either, because it's locked through the BIOS to IDE emulation mode -- but I've chosen a modern enough drive that it shouldn't be a problem. The firmware should do a completely adequate job of garbage collection on its own, and even if the performance is degraded compared to what the drive's rated for, it should still have absolutely no problem saturating the UDMA-100 the i815's IDE controller is good for.
As for exactly what variety of Win9x I'll be going with, I've decided tentatively on Windows ME pending final system stability, trying my best to stick with all VxDs since ME's problems mostly boil down to issues with mixing VxDs and WDM drivers. This is 100% not a DOS rig, between the less-than-ideal sound situation (the Vortex2 has a DOS driver, but it's completely emulated and sounds awful) and just having a dedicated machine anyway in the 486, I'm not bothering with anything non-Win32. It's a bit of a change of scenery from the copy of 98lite my 486 runs. As for whether I'll run the 98lite shell swap tool on ME, I'm leaning toward not, because the version of Shell32.DLL it copies over freaks out some later software that's supposed to be able to run, and having to hex-edit stuff to change references from Shell32.DLL to Shell32.W98 is a pain. It wouldn't be worth the miniscule speed boost it's good for on such an already fast machine for the task at hand, and really would just be for aesthetics -- which, to be fair, I do prefer the 95 explorer to the IE "enhanced" one, but it's not worth the trouble.
Why 9x in the first place? Well, it's era-appropriate, but also because the Vortex2 sound card it's going to use has very lackluster drivers for NT5. On 9x you get full hardware acceleration for 3D APIs like EAX and A3D, whereas on 2000/XP you just get stereo output. The Voodoo3 is in a similar spot -- sure you can get Glide support on 2000/XP, but it's through third-party drivers and in general they just kinda suck on NT. And there are some games that have weird issues on NT5 that don't happen on 9x.