The problem with inexpensive 4k TVs, or 5K IMAC screens, is that they are horrendously inadequate when it comes to the most important facet of picture quality; contrast.
I read a review on the the IMAC screen once, and the calibrated contrast ratio was around 1000:1. That is awful, and other than still images, I can't imagine the PQ is any good. Of course, the color accuracy is great, and the resolution is highly impressive, but contrast makes PQ.
I would rather have a 1080P OLED TV with something like a 20K:1 calibrated contrast ration, than a 16K IMAC screen with a 1000:1 contrast ratio.
I am sure the added resolution matters when your working with photos, but I have to also imagine you would want as stark of a contrast as possible as well.