4 GPU on 3 machines:

2x Nvidia GTX660         ~72Mhash/s each
1x Nvidia GTX660Ti       ~97Mhash/s
1x Nvidia GTX470         ~85Mhash/s

Never got into ATI for gaming so I'm using what I have !


EDIT: no tweaks, no OC on any of the cards. I played with it but 5% more mining wasn't worth the concern of running my cards too hot.