4K really is a leap over HD in terms of quality, I find it very noticeable. However, as my good buddy miXPture (
) correctly notes, sources of 4K content are scarce.
Devices that can drive a 4K display are also fairly uncommon, I think you need DisplayPort 1.2 or Thunderbolt to drive it at 60hz (as you should).
Regarding curved screens - it all depends how close you're sitting to the screen (and, I guess, how big the screen is). Please see below highly precise diagram I have spent dozens of hours on. Obviously, less "V" (viewing angle) is desirable.
