Re: Some Simple Maths
It also depends a lot on what the app is doing. A 3D game rendering at full resolution will need 4X the GPU power to get the same FPS (approximately) but pretty much any other app will not be maxing out the GPU. And, 3D apps don't have to render at full-resolution... they can still render at 1024x768 - which is just fine for 3D gaming on a small screen - and use loads more detail. It means you can render scenes at decent FPS you simply couldn't before.
And the CPU improvement is relevant in either case too - your game can have much better AI or whatever.