GEFORCE 6600GT AND 6600 are very good cards that are way better than the X600 generation of cards, but we have to remind you that the 6600 generation of cards are still not available while the X600s are. 6600GTs are available if you are a "privileged" member of the press that signs NDAs but for the rest of us mere mortals they are simply not to be had at all.
ATI is working on its Counter Strike RV410 card that will be sent to the "press" just a week after Nvidia reveals the scores. I guess that ATI might tweak its clocks if it feels necessary as it still doesn’t know Nvidia's final numbers. You better make your X700XT card faster then 8000 in 3Dmark.