The 8600GT is now a low-midrange card and will have to drop in price substantially when the ATI HD3850 becomes widely available. If you want a 8600GT, which is slightly faster than the older 7600GT, and a bit slower than the 7900GS, I would suggest to wait a few weeks to see what the price does.
NVidia is now in a bad spot with its 8600 line and they have nothing available in the short term to counter the HD3850. And in January, ATI will be coming out with the HD36xx series on 55nm process and DirectX 10.1 which will do further harm to the 8600 Series.