1. I highly recommend not upgrading now. Here are two links to people I have said this to already with lots of info as to why.
http://www.tomshardware.com/answers/id-2971952/upgrade-dual-770-980ti.html?siteFrom=EPR-8807#xtor=EPR-8807
http://www.tomshardware.com/answers/id-2971712/whats-difference.html
2. This one is easy. Dell Gaming S2716DG 27.0" --- It is cheaper than ASUS, and Acer variants. It is also not plagued by the bad quality control those two variants have in all the reviews. You will of course google it youself, and probably watch jayztwocent or linus tech tip videos, or read amazon reviews or new egg reviews. Bottom line this will come out on top in all of them. Until something else launches this is the best as of today 1440p with Gsync under $600