Source: MacWorld Macworld compared the performance of two (generally available) video cards with Mac Pro Rev. 2, the Radeon 2600 HD XT and GeForce 8800 GT.
As you can see, the Radeon is far behind in DOOM 3 and Quake 4. It does better than the Geforce with Unreal Tourney, a game in which the renderering effects seem ancient today.
It is also noted that in the first two games, the performance of the Radeon collapses in the high resolution while those of the Geforce are constant.
These may be explained these simply enough:
-- The memory bandwidth of the Geforce is wider than the Radeon. It does not get filled up by the high resolutions (as tested).
-- NVidia GPU is also much more powerful, better supporting the complex effects -- which go wron
