Why?
Just be advised if you're thinking of using the GTX760 as a PhysX addon card it's almost certainly going to end up a bottleneck so you'll actually get worse performance.
You can TEST this yourself, though it will vary by the game and by the setting you choose (i.e. Low, Medium, High PhysX). What's more confusing is that a game benchmark may show the opposite of what you get while playing.
Your best-case scenario is probably a couple percentage advantage like 62FPS instead of 60FPS.