I think that your title is what's throwing me off because it says just Reference GTX680 and not SLI 680. It does then say SLI MSI GTX 580.
So if your saying you are looking at a SLI setup of two GTX 680 vs. TWO GTX 580's then I'm going with the 680's. You will get good performance from the 580's for some time to come but the two 680's will allow you to do anything and everything.
I can't believe that a GTX 680 is going for $689 where you live.
I got 3 MSi GTX580 Lightning Extreme Edition 3GB so far it kicks ass, got my trifire 7970 and it kicks even more ass, so far the gtx680 (i'm aiming for a single zotac for the games and 2 galaxy 680) should do serve me well so I'm sure it will do the same to you (still planning on getting them)