I think the question is: what are the other specifications of your PC. It's not good getting a 8800GTX while still running an AMD 64 3500 :)
The other point is, I'm not really sure you're going to notice a huge performance difference between the R600s and the 8800s. It might really come down to the cost factor.
I think while shopping for any component, the best thing to do is do your research, make your choice, and don't worry too much about not getting the best component out there. It's too stressful doing that!