Using medium quality settings with 4xAA/4xAF enabled mixed things up a bit. At 1680x1050 the Radeon HD 4870 was actually faster than the GeForce GTX 260 by a small margin, while both the Radeon HD 4770 and HD 4850 overtook the GeForce GTX 250.
The Radeon HD 4870 remained slightly faster at 1920x1200 when compared to the GeForce GTX 260, while the Radeon HD 4770 and HD 4850 were able to overpower the GeForce GTS 250. Furthermore, the Radeon HD 4830 was faster than the GeForce 9800 GT with a very playable 60fps!
Finally at 2560x1600 the Radeon HD 4870 was impressive rendering an average of 52fps, making it 12fps faster than the GeForce GTX 260. This time the Radeon HD 4830 matched the GeForce GTX 260 with 36fps, while the GeForce GTS 250 managed just 31fps. Please note that if you compare the medium quality 2560x1600 result for the GeForce GTX 260 to that of the high quality test result you will notice that the performance was greater when using the high quality settings by 6fps. This is not a mistake, for some reason the GeForce GTX 260 and possibly all GeForce graphics cards are faster using high quality settings.