With the $300 price spread, I might as well just take that extra monitor cost and put the money into pricier AMD card than I would typically buy. I've run both nVidia and AMD over the decades, but $300 can go a long way in a GPU solution.
I have the Dell U3415W, which has the same resolution and size. It's probably the same panel, but it doesn't have G-Sync. It cost about the same as this one, too.
I have had problems with it because of the high resolution and wide aspect ratio. WoW runs fine, but the game is distorted on the far sides, giving me a less effective field of view than I expects. Most games and movie playback software won't run at anything more than 2560X1440, wasting the sides of the panel. Star Trek Online won't even run unless it is in windowed mode, and narrowed to the point of effectively being 2560X1440. It won't run in full screen 2560X1440.
I advise staying away from 21:9 screens for now, until software developers get used to the idea of them being out there. Otherwise, they're no better than a 2560X1440 screen.
$400 for the freesync? I think I've made my decision on which Gpu I'll be getting.
Until you experience stuttering below 46Hz...good luck with that. You will get what you paid for... And it's not $400 for the FreeSync version. It will be about $200 less than the G-Sync version. So you are still looking at paying $1100 for the XR341CK FreeSync version and it will have inferior performance. Tid for tad. The better gaming experience will be had on the G-Sync version, but at additional cost. PC Perspective did a huge hardware review on the differences between G-Sync and FreeSync and found the differences were significant and that G-Sync was worth spending the extra money. Cheaper is not always better, especially in this case. Don't fool yourself into believing otherwise.