I have the Corsair Dominator GT 2000MHz (Red ones) in my system. Testing and benchmarking them at 1333, 1600, and 2000MHz was interesting. There was a rather larger difference from 1333 to 1600 and a tiny difference from 1600 to 2000.
I also tested on Halo2 (1600 slightly better) and Heaven 2.5 (slightly better). I saw no differences going from 1600 to 2000 on those two tests.
Of course, I didn't play with the timings, let the BIOS do whatever was in the SP on the sticks which turned out to be 9-9-9-24. So, I run them at 1600 and know I have a lot of headroom.
Search the forums, I've seen a lot of folks post their results to tests like these. There have to be a million tests for this run by now that a Google should find...