The 770 didn't run 800x480 well, the framerates were generally bad. Let's not fool ourselves with that. The performance would decrease with increased resolution. What the cpu speed is doesn't have a direct correlation here. The display bandwidths are mostly separate, although you naturally need the cpu in determining what the content on screen should be. That's not the bottleneck in most cases: processing and determining the content doesn't take so much cpu power. Simplying the issue, one can say that the amount of pixels you can push on screen per second is fixed. The more pixels each frame has, the less frames per second you can do. If the device would be 480x320 resolution, it would be a lot faster in many cases.