Still to vague... *nix contains unix, irix, and of course linux... SGI and unix machines usually have a much lower 'processor speed' defined in mhz/ghz compared to an x86 system... so if you're just comparing mhz then the sgi computers would kick any x86 box....
If you're talking about latest technology, an sgi workstation will still kick any x86 box at graphics....
My guess is that you're really looking for linux vs windows on an x86 box...