Dont worry about it. Benchmarks arent everything. As long as your games look good and they dont glitch or lag then everything should be fine.
Basically. Benchmarks insanely stress your components. I got a FX 5700 256mb card and I can run doom fairly well. High settings, 800x600 resolution, no AA or AF though
But I haven't gotten to try out doom now that I have an OC'd processor and my PC3200 RAM allowed to run at it's full capacity. It had been underclocked to PC2100! All in all you still got a pretty good card and the 6600 should be coming out fairly soon and I believe will be released for $199 and that should perform quite well.