I think the 8600gt is a little better.
Because I think the 7600gt performed very similarly to the 6800gt, and as you said, the 8600gt is a little better than the 7600gt.
Which side of the argument are you on?
I couldn't find neither the 7600gt nor the 8600gt, but as you can see, the 7600gs is barely slower than the 6800gt. So it'll get a little better by upgrading to 7600gt, and then again to 8600gt.
EDIT: I didn't realize that the link didn't really work. It didn't save the settings I used. But you can look yourself I guess.