I'm guessing this is likely a driver issue as I'm running the new NVIDIA drivers that were released a couple weeks ago.
That said, I've had no problems with any other games since installing my GTX570. I used to have a 560TI, but it was giving me issues and the deal I got for a brand new 570 was too good to pass up considering the 560TI was taking a ***. Anyway, I remember playing Just Cause 2 on my 560TI at High settings with a framerate that stayed between 55-60 at all times. I've lowered all the settings possible in this game with my 570, and it just will not budge lol
I'm getting between 25-35 on some of the lowest settings. Roll back drivers?