2x780's won't last you on 1440p unless you want to start turning settings down in game!
I have 2x780's and also run 1440p Asus Rog Swift and have a Samsung 60hz 4k monitor as well, Latest games play but I still have to turn things down, Also the 3gb vram is now showing it's ugly head in the latest titles. 1080p no problem, 1440p playable but 780's now showing their age, 4k some games playable but basically you have to turn down a lot of settings and anti aliasing all the way otherwise you will black screen from not having enough vram.
I would wait it out for 390x and 980ti, Either will be the card to have for 1440p and 4k gaming especially if you are only after 60hz(60 real fps) 1440p with max in game settings.
I basically haven't touched gta v or witcher 3 on these 780's, gta v played a bit of single player and online, have to turn things down ruining game(I want it maxed) witcher 3 runs but 780's sli max settings I only get 30-40fps and that's just the start of game looking out the balcony so I didn't bother playing any further, 30-40fps is not enough for my liking but each to their own.
Also both cards were running at 82c and 80c in witcher 3, that's with decent airflow in case and reference 780's blowing air out the back of case not custom coolers blowing hot air inside.
Wait it out mate, Only a few more weeks to go before new cards are announced.