As malacai said:

Overclocking the Pi2 to Pi2 setting made PSX games run pretty much flawlessly for me.

N64 is not so much a speed issue as an optimisation issue. If you turn down the resolution to 640×480/VGA the games getting that nice retro fuzzy look :) and also run rather smooth.

To check which emulator is best to use for which game (if it works at all) check this list:


Hope this helps!