Depends on what you mean by 'processing'. I don't have any experience with the larger, or expensive chips, but do try to keep up on my reading. The best I've seen for video, are monitor test patterns, text, and a few lower resolution arcade type games. And these all seem to really stretch the capacity of the chips to the limits. Don't usually spend much time looking at the higher end chips, still sort of learning with them small and cheap. Might check the Atmel site, or AVRFreaks and see if there is something useful.