Don't know much about 4k monitors, except that they cost A LOT.
I roll with the Eisenhower principle, "Bang for Bucks", so I stayed with 1080p.
I am using a Sanyo 55" 1080p 120hz, it cost under $400 on sale at Wallyworld.
Vid card is a GTX1060sc, game settings maxed out, FR's are always way over 100, and it looks FANTASTIC to my eye!
Like anything else, ya pays yer money, and takes yer chances. Good luck and happy shopping!