NVidia cards only run PhysX. AMD cards don't run it.
Right now with all the crypto coin mining going on and since AMD's rock at it, you could probably sell that 7850 for a good price right now. Used 78xx and 79xx cards on ebay are going for high prices. I don't live in a huge city, but there is people online on kijiji looking to buy all AMD cards just to either flip for a profit or use themselves for crypto coin mining.