[quote name='LinkinPrime']The 8 Series support DirectX 10 so yes they are better.[/quote]
The 8500GT supports DX10 as well, but it sure as heck is not better than the 7600GS. As for the 8600GT(s)...eh, you're better off getting a 7900 on sale, with the same or better performance for less $$. Or, as other have said, spend about $20-30 more and get the 8800GTS, since it mops the floor with the 8600 series.
Price vs Performance. Anandtech has a write up on it in their Video section. It was a wash between the 7900 and 8600, with the 7900 outperforming it in several games.
Go to Anandtech and read the Final Words on their review, as it is similar to others that I have read. The ATI 19xx series beats the 8600 as well.