Even though the model number 8600 sounds much bigger than 7600, the GeForce 8600 GTS is only a very minor upgrade to the GeForce 7 Series. I would say it mainly adds new features like Shader Model 4.0 and support for accelerated HD video decoding.
When looking at the card's performance it is comparable to the X1950 GT or Pro. Especially the X1950 GT can be found a lot cheaper, but it doesn't have DirectX 10 support. If you are looking to spend a bit more money, to have a powerful card for this year at least, you should look into the GeForce 8800 GTS 320 MB which has all the great G80 technology, but isn't that much more expensive.