I have the same stuttering problem with my GTX260, Core i7 860, 4GB RAM and Win 7 64bit.

Unplayable on ground. Rolling back drivers etc. as well as the mentioned NVIDIA control panel tweak didn't work.

Only if I set the games graphic quality to the lowest possible level in the game's option slider it runs smoothly on the ground.

If that won't get fixed soon I will not subsribe and cancel my preorder.