With both SLI (working) and Single GPU mode, the performance hit is big. Especially in the open area at the end of the demo (framerate there is 30-45 and feels really choppy).
Even with normal PhysX, the performance hit is almost similar (yeah the physx support is enabled in CC
Simply put, i prefer constant smooth framerate than some minor effects with such a performance hit.
PS: Tried both 190.40 and 190.56 drivers