The ATI x700 is about the same as the Geforce 6600GT, yet the most 6600GT cards can be overclocked an awful lot, and 3D benchmarks don't actualy matter for real gameplay. You'll find that the Geforce 6600GT is actually slightly better and excels in areas.
The Geforce 6600GT is actually rather cheap for a mid budget video card which will play the latest games great at high resolutions and settings