Best setup for 2560x1600 res sli or xfire

Hey everyone,

I just sold my 6970xfire and I wanna upgrade to the fastest multi card display. I game on a dell ultrasharp 2560x1600 res.Im torn between the gtx 680 sli or hd7970 xfire.Which is the best option? I still have a lga 1366 mobo with pci express 2.0 but from what ive heard it`s not a difference between 2.0 and pci express 3.0 for either set up.(please correct me if im wrong.)

Thank again for your time