I've a PPC 9600 G3 520Mhz/1.5GB/80GB with Radeon 7000 and Voodoo 5 5500 PCI, great machine! Unreal still looks amazingly good - especially the first level, oh and the music.

Another good choice IMO would be a 6500 with Voodoo 2 card installed, G3 preferable. A beige G3 would be fine too.

For 68K gaming, an LC630 is a good choice (crap case, but Marathon is somewhat hardware accelerated!).

JB