I have poor eyesight and need to sit closer than normal, and I find 27" to be just a tad too large. In my home-office setup I have a decade-old 24" 4K IPS panel that is the perfect size, and I dread the day it gives up the ghost because apart from some very expensive professional monitors, no-one seems to make them at that size and resolution class any more.
2x dell 2415q's is my favorite setup I've ever had. I hope that some more options for high-dpi 24" monitors come out in the future.