Just ran a small game I made test C2 and the results on iOS5 were impressive. It ran really well, over 30 FPS for sure.
But my game was intended to be light, so I added a few more objects and made the biggest sprites rotate with every tick. There were no significant changes in the framerate, although we made a garbage collector to help improve the performance and seconds before running it we had some slow down.
I didn't test sounds on this game. Nor the recent physics.
I am very impressed by the results, now we just have to wait for these improvements to go live. :D