Yep think your spot on with OS's
Either a killer 9x machine or early-ish XP system

I've a S478 98/XP dual boot machine, it's best use is running games like GTA3 in the more stable XP.
That said I'll admit I still prefer 9x gaming on my P3, it has more nostalgia
and prefer the S775 for XP with where I can max out all detail settings.

still it's nice to have and yours's will be more interesting with RAMBUS, I'm using boring SD ram 🙁

Other options is setting one up as a Windows 2000 or 2003 server.
Or what I would do is run one up with Windows 2000 Pro and use that for Win9x gaming. You get better stability and still has a retro feel and you still have the R400 for games that don't like 2k.
I do most my 9x gaming in 2k now but that's on a dual P3 rig

Thanks for reply!
Not even heard of using Win2k Pro for 98 Gaming.I do Love that OS,Rock Solid!
Is there a compatibility Mode in Win2K,or how does that work?

Mostly it works just like XP, so you can set compatibility mode though the shortcut just like XP. But for the most part the games just work, only ones I own that don't are:
Need for Speed 3, 4, Porsche (XP patches may fix this, I've never really tried and just play in 98)
Return Fire, Early Win95 game so fair enough
And I think Road Rash may have had trouble, cant remember on that one.

I suspect alot of the games that do work in 2k will also be fine in XP, but then you loose that retro feel (plus a bit heavy for my P3)