Steel_Nugget :
Actually if he has room and has the second card as a PhysX GPU he will see increased performance on games that use PhysX.
Probably not actually, I have tried it with Borderlands 2 and GTX660Ti's and there is no performance increase at all if one of the cards is dedicated to PhysX. The only performance increase comes when SLi is enabled and PhysX is set to "Auto".