Earlier quoted context omitted.
2560x1440 on a 27 inch at a reasonable distance is pretty darn close to optimal IMO, so 4k, to me, is for 34" monitors (but 27 inch I feel is optimal on 60-75 inch desks, which is what I usually work with, so 4k rarely matters). I'm with you on accurately calibrated monitors though! God most of them suck out of the box.
I never get comments like these, as if the text just gets smaller as the resolution increases, rather than what actually happens (the text gets crisper). 5120x2880 is so nice because you can’t see the pixels and words almost look like they are on paper.
You need a higher PPI to make anti-aliasing work on screen (finally looking nearly as nice as print).