That’s strange...
I’ve a Mac Mini, early 2009, Resolution 1920 * 1080, but all the other settings normal/low, and it works fine.
Some lags with the newest patch, but i can still play...
Same GraCa, 2.0 Ghz DualCore...
I think there's a problem with the m series drivers and hon. My friend's laptop also did the same thing, until he got a newer one. My laptop still does it during large fights and just tanks it to 5-10ish, and it can run crysis on medium at 30fps. So I dunno, post on their forums see what they say and post back here when you get an answer.