The newer processors have more fine-grained "Turbo Boost" so if you're using single-threaded or two-threaded programs, they can clock up to 3GHz+. I looked on Apple's site, but didn't find which processor they're using. But from Intel's site, the only 2Ghz quad core seems to be this one:
http://ark.intel.com/products/76087/
So you could hit 3.2GHz single-threaded.