Recap
Although individual game results are interesting, especially when involving multi GPU systems, we calculated a performance index based on all tests with the same weight for each game. A score of 100 was given to the GeForce 9800 GTX in 1920x1200.

Without antialiasing, the Radeon HD 4850 jumps in front of the GeForce 9800 GTX. However, the GeForce 9800 GTX v2 shows an average gain of 8.3% compared to the previous version which isn’t bad for a frequency increase of 9%. For this reason, it surpasses the Radeon HD 4850. Otherwise, its bigger sibling, the Radeon HD 4870, has no problem beating the GeForce 9800 GTX v2 as it is even ahead of the GeForce GTX 260.

On the other hand, with antialiasing, the Radeon HD 4850 is ahead with an 18% lead on the first GeForce 9800 GTX and 11% on the new version. Moreover, it surpasses the Radeon HD 3870 X2 which often has problems with this filter. As for the Radeon HD 4870, it comes close to the GeForce GTX 280.
Note that (only) for anti-aliasing indexes, results obtained in Bioshock and S.T.A.L.K.E.R. were not taken into account as the Radeons do not have support for this filter in these games. You can consult a graph which otherwise takes these games into account
here.