Needs some advice

Too much for a physics card. You could sell it and invest in a lower end card if you even need physics. Not many games use physics these days unfortunately.
That is a bit overkill for PhysX. I agree with the sell it comment. You could then buy something like a Geforce 650 for that purpose.
I read an article (no idea where...) that tested a 640 against a 580 for that very purpose and the 640 actually outperformed the 580 for some reason. He simply tested it using fraps and the 640 used for physx gave him higher frame rates. Plus that card doesn't need to be connected to a PSU. It's powered through the PCI-e lane (I think... 99% sure).