These emus are more than playable m8, Im afraid your question is a bit open ended as there are man emus Roms cpu speed etc
Here are my experiences with Emus:
Frodo (C64) Full speed Every game I play, can be made faster if Limit speed is turned off, My Favourite
Snes9xgp. I only really wanted this for final fantasy so with a frameskip of 2 its Ace
Genesis: Had problems with many roms on this one not speed issues just they wouldnt load, Have only had Taz and VF 2 working Taz was playable at about 80% orignal speed and Vf 2 was just shite!
Gameboy + GBC: Now this is where I love my gps smc! Every GB and GBC game I have played has been perfect in every way. I have no problems with anything... Other than pressing the L button that resets! rrrrgggghhh
I mainly use my Gp32 for the C64, GB, GBC and movies
I hope this gives you a better idea
Threaten santa for 1 they rock
Dean