Originally Posted by Xion X2
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.
Head on over and browse the forum, you'll find the thread on it. Jawed and a few others who know the designs of both cards and their short comings and strengths all agree that it is the number of filters used in applying AA. ATI has more than Nvidia this round where as last round, Nvidia had way more than ATI. It is these filters, lack there of, that cause the X600, R670 and R680 to all tank going from 2x to 4x AA. It only got worse with 8xAA. Nvidia on the other hand left their numbers the same since G80 which is why they killed the R6xx line in AA, but is now losing when you go above 4x.