Happily running a GTX 670. But I'm from the original crossfire days, when both cards had to be the same. My question is whether I can SLI bridge a GTX 670 with a GTX 780? Please advise.
In DirectX 12, you can mix and match GPU's in multi GPU configurations but it isn't here yet and the software has to support it. Another 670 is the cheaper upgrade path for you.