The guys at Phoronix throw down the numbers gauntlet & do a direct comparison between Doom 3 & Quake 4 on the same hardware, but under Windows & Linux. Pretty much confirms what everyone already knows: ATi's Linux drivers need some work.

"To be quite frank, the numbers speak quite clearly for themselves when it comes to the performance delta between the ATI Windows and Linux drivers. Even for the Linux drivers being based upon the ATI Windows Catalyst suite, the frame-rate performance under Linux is one of the critical areas for improvement in this graphics battle."