Again, please note that Nvidia owners can force AA but as you are about to see doing so does come at a massive performance penalty. We still wanted to include this figures for your reference. Radeon boards could not be forced into running with AA turned on.
The GeForce GTX 480 saw a 22% performance decrease when enabling 4xAA at 1680x1050, from the capped 121fps to 94pfs. Keep in mind if it were not for the fps cap the performance decrease would have been larger. The GeForce GTX 470 which was also capped without AA enabled saw a 43% performance drop. Finally, the GeForce GTX 285 suffered a huge 44% performance decrease when forcing 4xAA.
At 1920x1200 the GeForce GTX 480 lost 38% of its original throughput once 4xAA was enabled, while the GeForce GTX 470 became 50% slower with 4xAA forced. The GeForce GTX 285 also saw a huge 51% performance drop when forcing 4xAA.
At 2560x1600 we see more of the same. The performance hits came hard with the GTX 480 losing 47% fps, and we saw similar reductions across the board.