I currently have dual gtx680 classifieds that are nicely OCed and was debating upgrading to dual 780s or 780tis, would this be worth it or should I just wait till 20nm?
I believe most people would recommend waiting. Additionally, many places (such as here at THG) recommend only upgradng if you are going to be moving up 2-3 tiers. I believe your current upgrade thoughts would only be a one tier improvement.