I have been using emulators a lot, I have discovered great compatibility on pj64 (n64 emulator), it works with the majority of games just not the most advanced ones (like zelda and 007), neogenisis is a great sega genisis emulator with full speed and even a fast forward option, snes9x is a full speed snes emulator. fceau, even though I haven't tried any other nes emulators it seems to be fully compatible with every rom.
hope this helps
PS
C will never emulate on xbox as well as gc and ps2