first, I wouldn't recommend the ultrawides. I have a dell 2560x1080 (29") and while its nice I also have a eBay korean 27" 2560x1440 (diff PC) and that is way, way, way better. Tons more desktop pixels is just better. 2560x1080 is also just weird for game cutscenes, etc with big black borders.
Remember 4k is just starting to be big on TV monitors right now, its still not practical for attaching to a PC since HDMI right now is limited to 30hz at 4k rez, that should be fixed by the end of this year. By next year you should be able to pick up a nice 50-60" 4k TV that hooks up at 60hz via hdmi for $1-2k, which will be crazy good for gaming, especially if you attach a ps4 or xbone to it.
I currently run dell widescreen plus a 55" LED-TV off my PC, the dell for browsing and most games, the LED for movies/tv and couch type games (shooters etc). Its a great config, but you wanna be at least six feet away from the LED-TV to not fuck your sight up, don't ever try to make a 1080p LED TV your primary monitor.
You can also think about eyefinity, two or three 2560x1440 side by side with bezels removed may be amazing, eyefinity or not. Personally I think two 2560x1440s side by side (no eyefinity) is great, one for main display and one for all the extra shit, most games nowadays support windowed full screen mode and it lets you smoothly transition from one monitor to another.