the most you can do is physx card one of them. to sli nvidia cards, you need 2 exact gpu models(doesnt have to be same company just main model) the faster card then will downlock itself to whatever the slower card is.
Not at all... You could use both cards together to drive 3 or 4 monitors but you cant use SLI or surround. You can also use the 550 for physics as it is the slower card if you wanted.
the most you can do is physx card one of them. to sli nvidia cards, you need 2 exact gpu models(doesnt have to be same company just main model) the faster card then will downlock itself to whatever the slower card is.