I should point out that when you hit resolutions as high as 1024x768, then the phone's clock speed and hardware come into play. You'll likely need one of the later, faster phones to run 1024x768 without taking a performance hit. We'll provide a list of suggested phones when we get to that point.
At the current resolutions, the phones hardware comes into a play.
I would not mind an option (both for previous and future versions) for multiple resolutions, so you could scale it down if you needed a bit more oomph.