Hey guys! This is probably an old shoe, but after lots of weeks of researching I'am still not sure which monitor I should get. The monitor should help to utilice the GPU power. 
 
My specs: i7 4790k@4.5GHz, 16GB RAM, GTX 1080Ti FTW3@2GHz
Right now I'am using a Samsung S27D850T 27" as my main monitor (http://www.displayspecifications.com/de/model/98e76bb).
 
UHD sounds good, but 60Hz? I'am not really into competitive games or a lot of fast shooters. More then 60Hz is already on it's way, but way to expensive and a single GPU can handle barely 60fps in modern games. The prefered Monitor would be the Asus PG27AQ.
Now to 21:9 34". Obviously not as sharp as UHD but still needs a lot of GPU power to hit the 100fps, which should be much smoother then 60Hz. I haved heard, that some games don't support 21:9 right out of the box and you need to use programms to fix it or change some files. Cutscenes are often in 16:9 too and sometimes they just get stretched. The prefered Monitor would be the Samsung C34F791 (because of it's great panel and Quantum Dot)...but below 100fps you can probably see a lot of tearing, so there is also the Acer X34A with G-Sync.
Last there is 2560x1440@144/165Hz. 1440p looks decent and combined with the high refresh rate, this should theoretically be pretty good....BUT the manufacturers are using all this same bad panel from AU Optronics (atleast the G-Sync models). Doesn't matter if you take Acer, Asus, AOC, or Viewsonic...they all have very bad reviews because of Backlight Bleeding, dead pixles and bad quality control. 
 
Pretty hard to find the right display...
 
 

The budget shouldn't be a problem. About 1200$ is the limit. 

I recommend 3840x1600 however i have not seen an hdr gsync version announced yet, but there is a freesync version available. Im waiting on the hdr gsync version. This resolution plays movies with no black bars.

I personally prefer higher resolution to faster refresh rate (ideally both) but at the moment 4k/UHD is limited to 60hz on consumer panels.
 
I do not play many games that rely on higher refresh rates so the increased pixel density is better for me.

EVGATech_MDecker
I personally prefer higher resolution to faster refresh rate (ideally both) but at the moment 4k/UHD is limited to 60hz on consumer panels.
 
I do not play many games that rely on higher refresh rates so the increased pixel density is better for me.

+1 to this. What kind of games do you play? If it's online multiplayer like StarCraft 2, Overwatch, Quake Champions then faster refresh would be better. If you enjoy more single player games like Fallout 4 or Witcher 3 then I would go higher pixel density.