Dying Light at 4k looks epic. The part where you do the training took my breath away.
I do agree it's not very logical due to lack of GPU grunt right now but hopefully soon there will be a single card that can knock out everything properly at 4k.
I did used to run multi monitor but hardly any of the games I played really played well with it. Fallout looked awful and needed serious hacking around.
That's what it was like going from a 22" 1680x1050 monitor to the 27" 2560x1440 I'm using now. It took some time to get used to, but worth it in the end. I guess that can really be said for every screen upgrade I've done over the years. I still remember jumping from 640x480 to 800x600.