You can't just judge the cards by their clock speeds.There are lots of other and more important features
Anyway,CS5 benefits more from a fast CPU and a decent amount of RAM.GPU wise you'll be fine even with cards like GTS 450/HD 5750
I have 6 gigs RAM OCZ and a i5 760 OC'd to 3.6 and a gigabyte board. I am looking at the HD 5750. I can't wait! But if the speed isn't much of a concern, what should I be looking for in a graphics card for what I will be using it for?