the GT 310 will bottleneck the rest of the system, it is too weak to add-in and work as a bonus..
you might even get less frames because of it.
keep your SLi and make sure PhysX is set top AUTO.
stay like that until time to upgrade the SLi's...
what's the purpose anyways.?
when not playing a PhysX game (I know that Borderland's 2 and a few others will use PhysX) or benching PhysX software
then what will you be doing,,,,,, exactly, nothing.
it's a waste even if you have a better set of cards. SLi is better.