The Witcher: Enhanced Edition
There is no need for much commenting here. The Radeon HD 4850 and Radeon HD 4830 are the only cards to be able to deliver playable frame rates at high resolutions whereas the GeForce 9800 GT and GTX+ are limited to 1280x1024. Moreover, the Radeon HD 4830 is better than the GeForce 9800 GTX+ at 1920x1200.
The Elder Scrolls IV: Oblivion
There is no clear winner at 1280x1024, but the average frame rate of the Radeon HD 4830 is higher than that of the GeForce 9800 GT at 1680x1050 and this gap grows from 22% to 28% at 1920x1200.
The GeForce 9800 GTX+ is ahead in open scenes of the game while the Radeon HD 4830 is as fast as the GeForce 9800 GT. It is only at 1920x1200 that the ATI solution has an advantage in terms of bottom speed.