To start off, we have the unofficial standard among the benchmarking bean counters - the 3DMark suite. And things seem to be getting off to a bright start, with the GeForce 8600 GTS level with the Radeon X1950 XT in 3DMark05 at 1280 x 1024. But then the newcomer started to slip and by the time we reached 1920 x 1440, the scores were only slightly higher than the Radeon X1950 PRO. When anti-aliasing was factored in, the results were worse, with the Radeon X1950 PRO edging out the pre-overclocked GeForce 8600 GTS.
But this was in 3DMark05, where ATI mostly had the advantage. How about 3DMark06 then? Well, there was some improvement in ranking, with the GeForce 8600 GTS sandwiched between the Radeon X1950 XT and the PRO. It also managed to overtake the older GeForce 7950 GT card though when we tried the highest resolution of 1920 x 1440 with anti-aliasing, the GeForce 8600 GTS failed to complete the benchmark for lack of memory. The GeForce 7950 GT was dropped from this comparison, as it's not capable of running 3DMark06 with anti-aliasing due to NVIDIA's hardware implementation of HDR.
As you can see, the GeForce 8600 GTS is not exactly crushing the older cards like we might have hoped. Not to mention that the card we are testing is an overclocked version and not the reference card. In short, these scores are probably the upper limit of what you can expect from vendors.