So was the 6850 and now the GTX460 actually worse than your 8800GT?
Things you may want to look into:
Yes you can flash the BIOS and that might help you overclock your CPU better which might help in your games. As long as you follow the flashing instructions it is pretty safe.
Try disabling anything you can that is running on startup. Any extra software like file sharing, printer software, etc. If you got to Start>Run and type msconfig you can disable things starting up.
You may want to update your other drivers. One time I had a Logitech HID device that was causing horrible lag in certain games. I disabled it in the device manager after trial and error and suddenly everything was smooth.
And if you haven't already I would check the task manager (CTRL+ALT+DEL) to see if anything is taking more than its fair share of CPU time.
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