My game was all running fine on iOS, until I noticed that artwork using gradients looked very chunky, instead of smooth gradients. It turns out that whilst on Mac and PC 8bit gradients look fine, they have to be turned into 16bit artwork to look smooth on iOS.
Once I replaced gradient background artwork with 16bit graphics all looked smooth visually, but my game dropped down by 10fps! I had to go through all the logic and turn off any graphics that were not showing using Visible OFF to get back to 60fps.
So whilst all might look good on PC whilst developing a game, its always wise to test it regularly on the proper device.