He talks about only being able to run it at 30 fps on consoles. And simplified the engine for Rage, to be able to do 60 fps.
Doom 3 does 3 passes to OpenGL, and is very sensitive to jitter.
However on a LOW-JITTER linux kernel + config, you can run it gliding and silky smooth at 72 FPS, showing no taxation at all.
And it does not need to be the latest hardware. A core2duo + gtx280 will do.
For more info: http://paradoxuncreated.com/Blog/wordpress/?p=2268
A windows approximation can be found here: http://paradoxuncreated.com/Blog/wordpress/?p=1783
Windows will not run doom 3 aswell, and still drop frames, but it will help "microstutter".
Peace Be With You."
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