Death Prodigy :
Is it possible to have both?
High frame rates and sharpest screen shots?
And I wanted to ask:
Is 4K noticeable difference from 2560x1440?
4K is nearly identical to 1440p visually. The ONLY advantage would be slightly better anti-aliasing in some games, though modern anti-aliasing is starting to almost eliminate aliasing even at 2560x1440. There would currently be no advantage with TEXTURES since games don't have textures that high (not even 1080p usually).
However, attempting to achieve a good frame rate in modern games at 4K + best anti-aliasing isn't really feasible.
Beyond 2560x1440 we're starting to enter the point where the advantages of the higher pixel count are fairly small, but the disadvantages in cost and performance are fairly high.
I have a 2560x1440 monitor and play most games at 1920x1080 because they just don't look much different and I wish to achieve 60FPS. I do play some "god", top-down games, like StarCraft 2, CIV5 etc because they do look better (mostly the HUD/Text); however these top-down games tend not to be as demanding and I think a single GTX770 can handle pretty much any game of this type at 60FPS, 2560x1440, Max Quality.
SMOOTH gameplay is very important too (many would say the MOST important). In fact, the better the visual experience the worse any stutter, lag or low frame rates are going to jar you out of your immersive experience.
My recommendation still remain that you should look at a 2xGTX780Ti, and G-Sync 27", 2560x1440 monitor.