So what kind of board are you running that runs the 6800GS/GT good? i hear it has problems with nforce3 boards?
The 6800GS is in my bro's rig which is using some "Biostar" board- and yes it IS using the nForce3 MCP. And it runs FANTASTIC. I even unlocked the "masked units" and it still runs great.
My 6800GT is running in my K8V SE Dlx which using the VIA K8T800 chipset. No compatibility problems there either. I'm betting that whole thing about the nForce3 and the GF6 cards not working was some sort of a driver bug. Infact, I asked about it a while ago and somebody pointed me to a thread where they had resolved the issue. Not sure if that was at this forum though. Anyways, it works, and that is what matters so far as I'm concerned.
The 6600GT is a sweet card, but to meet the constant 85fps you probably would have been better off with the 6800GS. Then again, the frames you're getting aren't even half bad. I wouldn't be complaining at all. Anything above 60fps and your eyes (more than likely) wont detect the increase in fps. A friend of mine is running nothing but 6600GTs for his gaming rigs and he loves 'em. Slap an NV Silencer on that thing and it'd probably oc like crazy as well. You should enjoy that card, and I doubt that you'll be dissappointed once you really start messing with it.