plus there would be several factors with the overclocked list, like room temp, and some of the same cards having different overclock potential, and case fan positions
The 7900GS is more powerful than the 8600GT but this goes by everything which includes the DX10 as well as the overall image quality of the 8 series are better. I said that this isn't exactly based on performance since some cards overclock better than others. This is pretty much stock since different people get different overclocks. However in the end performance goes to the 7900GS but I believe the better image quality and DX10 support puts it above it on the list. This is not overall FPS but a combined list of everything, what it does is put you in the right range of what cards to look at not tell which is best for your needs.