Seems ok in 3D Mark 05, but kinda low in others. This is what I get on my GFFX 5900 flashed to 5950 @ 515 core, 985 memory:
3DMark 01', 03', 05' @ 1024x768 32 bit:
I have the same basic computer you do except for the video card.
I thought that the 6600GTs scored around 8000 in 3D Mark 03. Maybe try overclocking your video card. I read that the 6600GTs should overclock nicely. You do have great overclock on your CPU