Can't speak to 4K but I recently switched to 3 2K monitors (2 vertical on either side of a horizontal monitor). And I quite like the vertical monitors (My setup resembles a tie-fighter) even though I had resisted trying them for over a decade now.

I still have 1 1080p screen attached (just for NVR viewing) and if I drag my IDEA (code editor) window from a vertical monitor to my 1080 then it takes up over 3/4ths of the width. Just to restate that a different way: I gave up less than 1/4th of my screen width but got ~3x the height (just for the 2 vertical screens).

My current setup looks like this with 1 & 3 being vertical, 2 being horizontal, and 4 being my old 1080p horizontal.

    |   | | 4 | |   |
    | 1 ||  2  || 3 |
    |   |       |   |

I have my 2 vertical monitors divided into 3rds (top, middle, bottom) and have keyboard shortcuts to move windows between each region (coupled with a shortcut to move/resize all windows to their predefined default locations). My code is always on monitor 3 taking up the bottom 2/3rds (I find that using the whole height requires too much head/eye movement). I like to use the top 3rd of both vertical monitors for things like chat/reference.