I'm running an early 2011 15" 2.3GHz MBP with 6750M running OSX 10.6.7
I'm using a minidisplayport to HDMI cable
Its connected to a Dell S2409W monitor
The problem (like the OP) is that when i set the display to 1920x1080 in the game video options, it outputs 1080i instead of 1080p and so my display goes nuts flickering, overscanning, and looking like crap.
This hardware setup works perfectly in SCII in windows and for all other purposes on Mac. Its just this particular game in Mac.