lol Better at what? They are different cores, and different manufacturing processes. As far as comparing them in bench tests, I am not sure...cuz the 6800GS uses 12 pipes, the others do not.
Yes the core are different meaning that speeds can't be used as a true comparison. You would have to look at stats for the different cards from test results on somewhere like futuremark. One thing the 6800 doesn't have is High Dynamic Range Rendering Support, whereas the 7300 and 7600 cards do.
well i know the 7600 and 7300 have 128 bit memory but they have better applications on it like intellisample (or something like that) etc