Just so you know - don't put PhysX on "automatic" in your nVidia Control Panel. I don't know how it's called in english versions actually, but I'm talking about the place where you can choose from CPU PhysX, GPU PhysX and Automatic.
I have never had any problems or something when it was on "Automatic", but playing Borderlands 2 I noticed some strange things. I haven't any performance problems or something (GTX 680 FTW), but when messing with settings instead I noticed that putting my PhysX settings on "GPU" granted me with more PhysX effects (for example my character is "interacting" with cloth - when I had this set up on "Automatic" and I walked past through cloth there was no interaction between my character and it).
English isn't my native language but I hope that you understand my point :) I had PhysX based on GPU, not CPU when I had it on "Automatic", but changing it to "GPU" adds even more PhysX effects.