Performance can range from equal to PC to outright unplayable, as with all things it's down to how you make it, a graphics heavy game with tonnes of physic objects and particles is just not going to run well (Probably on anything!).
Different horses for different courses, you can make a good performance game with C2 (The best example that comes to mind is Mortar Melon by Mudvark)but you're going to have to design with mobile in mind.
3) See above. Generally speaking it's not very good if you're making lots of stuff react with each other, but I've made a few tests that had around 5-10 objects running physics and the performance was fine.