I think I would first look at the "system requirements" of the
software and go with the "recommended" specs and then bump
up a notch or 2 just for good measure.
I like the Gigabyte cards, I have the 9600 pro and got it over
other cards of the same chipset just because it was fanless.
Gigabyte makes good products-IMO..
Go here for some info: It can be a mind-numbing exercise
keeping track of the changes in the VPU industry.