I only use what I have which happens to be a single GTX460, and while I wouldn't normally have mentioned it  ...I get up to 150khs mining Litecoin and more if I overclock it but at the moment its summer here and so with no special cooling I am somewhat limited by GPU temp. I try not to run it over much over 80C.
Mining Max I get 50ghs lol sounds impressive, but not economic of course.