The 9800GTX is basically a 8800GTS w/ better memory and a few extra features. You will pay a premium for the 9800GTX as it's new. The 8800GTS is really the better buy and will OC very well on the GPU end, the memory not so much. I'm Extremely happy with my 8800GTS and they have come down in price since I bought mine. Many of them have rebates as well so look out for them. Its the better deal really. If you are willing to pay the premium for the GTX go for it. Get the GTS is you want the best bang for your buck.
If those benchmarks were true, that a 8800 GTS slightly performed better than a 9800 GTX, then your better off getting a 8800 GTS then. To me both cards are almost the same anyway, and a 9800 GTX only performs like 5% better than a GTS isn't even worth the price.