I've seen a math-related bug that the overscan settings in a/v wizard don't exactly correlate to the size of UI2. They are close though. Regarding the speed, which UI are you using? UI1 is pretty fast even on really slow boxes. I've run it on a 300Mhz before. UI2, however, requires the video driver to support XDamage at least, and XComposite if you want alpha blending. My nVidia 6150 does this and the response is very fast even with alpha blending, and cpu stays below 10% always.