Last I read the 8600GTS is on par and slightly better than the top of the line DX9 parts eg. 7950GT and X1950XT.
More like a step down. i.e. 7900gs/x1950pro(barely)
http://www.xbitlabs.com/articles/video/display/geforce8600gts_9.html#sect1It matches the x1900xt in one game - oblivion, and struggles to meet up with the x1950 PRO in a couple.
Nvidia dropped their ball on this one. I really hope they make a 64 unit midrange card (with 192/256bit interface), because this just doesn't cut it.
For those with newegg availability, the x1950 pro is
just over $100. While it doesn't give you dx10, it's faster in any current game. I fear that dx10 will be greeted in the manner of dx8 years ago.
Remember when the geforce 3 and 8500 hit? dx8 was so new, most games tacked on a crappy extra feature to call them dx8 games. e.g. ut2003 and morrowind threw in crappy watter effects. With smaller development houses, I think dx10 is going to be another one of these "tacked on" minor feature sets for some time. taking advantage of both dx10 and dx9 will be a pain for smaller companies.
What that means (and how it relates to the 8600) is those buying the 8600 knowing it's a bit slower than the x1900pro, may find themselves disappointed if games don't make the dx10 necessary features compelling enough.
I'm hoping the 2600xt is better (though not expecting it)
