erm Speed Difference in Quake3 is ZERO ... Q3 is pure OpenGL. Microsoft never complicated the fact of Shaders, because Shaders are originally OpenGL hardware based - but based upon standard Layer Textures which 3D Packages have been using for years.
Whole thing is silly really and quite simple to emulate simple ones without much trouble.
As for Linux and Unix - i've used several and i've found them quite easi to crash with the slightest thing - and unlike windows they don't tell you they have either. They just get "stuck" ... atleast with windows it tells you what the hell has happend and that you can't do a damn thin about it
Windows also runs a special mode of ScanDisk which checks the Operating Systems status and prevents the crash from reoccuring - WindowsXP and .Net even send off bug reports they compile when they update and whenever you tell a program to so you don't have to file a report yourself and all the technical info Microsoft needs is right there.
I mean Linux|Unix are nice and all ... but really compared to the latest Windows - I'll go windows everytime, because the bugs are fixxed, might not be overnite but a bunch of nerds on a website - but they are done and it has maximum compatiblity.
The WindowsNT Operating System is actually far more stable than almost every other OS out there - always has been.
The real problem which causes the crashs is actually the legacy compatibilty and trying to work around DOS still.
Its about time they just rewrote it and emulated everything rather than environment swapping.
You really want to see a DirectX 9 performance jump, run Black&White ... on my Laptop the FPS jumped from 45 to 67, this is with full graphics at 800x600 and the mouse no longer lags.
Other good ones are using the Unreal2 Engine, like UT2K3 and AAO etc...
Anata aru kowagaru no watashi! 
