I asked around a bit here during past weeks and gathered some helpful tidbits. I always thought, technically iOS and OS X should still be close, also giving back to each other etc. Apparently that's true. I also asked about optimization and GPUs and everything.
How about speed of the OS? I never really understood why speed within the 2D OS can be slow, sluggish at all. This is no longer 1990 and computers went a long way ever since. A computer can handle Doom 3, it is old, still fast, animated menus etc. But iOS 7 is sometimes a bit slow on an iPad 4. Inifnity Blade isn't.
Just ask around on more general questions, too. Just started to get into iOS a year ago...