Can I use 2 different video cards for SLI?

[ShinReine]

I currently have an GTX 650Ti. If I get a later model (750+), will it work?

 

[Gam3r01]

In order to SLI it has to be the same base architecture and card.
650Ti and 650Ti, 760 and 760 and so on.

 

[ccampy]

No same model only you can have different cards e.g a MSI and a evga but both have to be the same chip a 650ti in your case