Well when you upgrade to a different card, what you thinking (I'm assuming) is that you want to dual both cards up... "SLI" Dual graphics. SLI only works with the exact same chipset, example two 580's... or two 760's. It will NOT work when you buy a 760 and try to SLI it with a 580. Simply won't work.
And what I was saying as it would become a physX card .. is some games have Nvidia's special effects called "PhysX" it adds... well more physics to select games.
In the Nvidia control panel you can setup that exact card to deal with JUST the physx rendering. Nothing else... So basicly, if your playing BF4(Does not use PhysX)... it theoretically is a paperweight and is hogging up more power