I have a 27in Quad with the 5750gpu. I play SC2 and Counterstrike Source, they run perfectly with no problems at all. I play them at native 2560x1440, with graphics settings at Medium. I think as long as gpu drivers get updated and all that you should be fine. If you are getting a computer JUST for gaming then get a PC you will be happier, if you are getting a computer for LIFE and all its necessities and your going to game on it then get the iMac, even though i do suggest the 27in...i have a small desk as well and it does not take up as much of a footprint as you may think