Mate, you probably don't have to even upgrade. If you want to go all out though, go for either an R9 290X or a GTX 780ti. Those are the top cards at the moment. However, your GPU is really good, and really doesn't need an upgrade until around 2 years from now. Hope this helps!
Thanks! I only ask because of The Division. Game looks amazing and got to have the goodness! >.<
I know man! Looks amazing. I do agree with the man above, though. SLI would be really powerful and last A LONG TIME, but SLI can cause more problems in game. Especially for a new game, SLI support does not come out right away. Hope this helps!
680 is a good strong card, the 770 would be a bit of an upgrade though would prob want to go 780 or 780TI or wait for the new 8xx Series that is due out soon to see any real gains that would be cost effective