I have recently upgraded my GTX260 to a GTX560 ti for use in Rift. I have not seen any increase in frame rate at all. On top of that, it seems to get bogged down more than the 260 in high population areas and boss fights. At first I thought this was a software issue. So I purchased a new hard drive and did a fresh win 7 install on it. Exact same poor frame rate.
I am running the 266.66 drivers (the latest from nvidia).
Mobo- Asus P5q-Pro
Proc- Core2 Duo E7200 @ 2.53 ghz
64 Bit Windows 7
4 Gb Ram
Psupply- 850watt SLI ready
Nothing is overclocked. I never tweaked any clock speeds.