What to do with extra GPU that is in the same series as the in-use GPU

[MyKeyblader]

So I use two systems primarily for gaming and surfing the web. One of them has a GTX 650(non TI) installed and the other one has an HD 6770 installed. I have a GT 620 and an HD 6450 currently not in use. Is there a way I could use these cards to improve performance or for calculations or physics? I've heard of using a second card in PhysX rather than SLI mode, but I don't know if my situation fits into that setup.

 

[Gam3r01]

You can use one of the two to run a second (or more) monitors to take stress off the primary card when gaming (this would improve FPS slightly).
Or you can do Physx with the 620, that being said unless you play games that support Physx it wont make a difference, and the 620 is very weak to begin with.

 

[photonboy]

PhysX dedicated card:
If the card is too weak the game actually runs SLOWER because the main GPU sits waiting for it to finish calculations. Almost certainly the case here.

Second monitor?
Sure. Make sure the second monitor is attached to the GT620 though. If you have a second monitor.