Also just to add, the claim of 31k pmk.s was made by elcomsoft and not by pyrit. This is a profit based company who grossly overexerted the figures for ntlm cracking as well. They claimed 1.3 billion ntlm per second on a 295 gtx when if fact it is more like 600 million.
ATI has also always had the worst linux support as well, whereas nvidia has a entire section working on CUDA/linux type stuff at all times. Not to mention none of the other cool GPU tools work with ATI. I will stick with the team that is in active linux development, even if it mean getting a few less pmk/s
Just my 2 cents
If you are interested here is a breakdown of my latest CUDA/Nvidia box