Originally Posted by XMAN52373
Filters. This was discussed at B3D.com. The 4850/4870 have more filters than the 260/280 does and thus take less of a hit going from 4x to 8x. It is filters that caused the R6xx line to tank when movin from 2x to 4x AA where as the G80/G92 suffered little to no hit. Nvidia left the filters alone going from G80/G92 to G200 where as ATI increased theirs a great deal going from R6xx to R7xx.
I'm not saying there aren't other factors; I'm sure that architecture plays into it. But if frame-buffer were a limitation with 4870, then you still wouldn't see such a small performance drop-off in going from 4-8xAA at high resolutions. It would take more of a hit since AA eats up VRAM.
From the very few benches I've seen, however, it looks like 2560x1600 may cause some issues. That shouldn't concern the majority of the population who don't have those monitors.