Which MBP are you talking about in particular?

I used to play SC2 on my ex geforce 310m macbook 13, mid - high setting without AA, very smooth (but bootcampp of course).
Try to avoid playing games directly thru MacOSx. I had to lower the resolution + low settings to get playable framerates.

I assume both of the games use almost the same game engine

anyone 2011 15inchers played diablo 3 on OSX? Wonder how it perform