I know you've already picked a solution but I would like to put in my two-cents as well.
I also have a 1080 and was in your situation not too long ago, I was going to go with two monitors, one 2k and one 4k for games that run well on 4k I would use the 4k monitor, and in games that don't I would use a 144Hz 1440p.
I got talked out of that because of all the reasons 4k is not very good right now (you need more than a 1080 to hit 60fps in most games and that means a Titan XP and a ridiculous budget plus you are limited to 60Hz, until Asus comes out with 144Hz soon, but even more already nonexistent single-gpu power to hit that.).
Anyways I got talked into UWQHD, and I am very much looking forward to it. I plan on getting the Acer Predator X34P when it comes out and trying out my 1080.
UW doesnt come without hassles and a lot of games don't natively support it, but there are plenty of addons and mods that will make it work.
144Hz is nice, but I think for me I will take 100Hz UW.