8600GTS is similar to a 7900GTX. It just cost way too much. I think all that's disappointing about it was its launch price. These cards even had a big advantage over G80 with VPE2 or whatever it's called.
Your right, I got it and the 8600GT mixed up with the GTS. And the 8600GTS was on average about as good as a 7900GS, still a fail in my book as the GTX and both GTs(7900/7950) were faster. And all 3 are conciderably faster than a 7900GS.