Replacing 8800GT with a GTX 460 - FAILURE

I was using an XFX 8800GT 512, and just replaced it with the EVGA GTX 460 768MB. Testing with Modern Warfare 2, and Age of Conan, my framerates actually dropped severely. They weren't great to begin with, but at least playable using the 8800gt, but they are actually performing much worse at the same settings, as low as 10 fps for extended periods. My method of installation was this: I uninstalled the 8800gt drivers first. Then replaced the card. Yes, both power plugs are plugged into the card. I then installed the new drivers from the EVGA support site. Tested the games, horrible results. Then I uninstalled the drivers again, and this time used Driver Sweeper. This time I installed using the drivers from the CD, as well as reinstalling DirectX for the hell of it. No difference, still horrible framerates. I tried installing the beta version of the latest drivers from the Nvidia website, and same results, mostly. For about 10-15 minutes I was getting about 30 fps on Conan after installing the beta drivers, now today it's back to about 10. Modern Warfare is still unplayable as well.

Even though motherboard and processor are pretty ancient, why would I actually be getting worse performance? Shouldn't it at least be equal or better? Everything I read about this card indicated to me that going from the 8800gt to the GTX460 was a huge impovement.

EVGA GTX460 768mb
Intel core 2 duo 6600 2.4 ghz
Intel DP965LT motherboard
4 gigs ram (3.5 usable), ddr2, unsure of the brand
Coolermaster 450w PSU
Windows 7 ultimate 32 bit