I’m using a 4K 28” (I didn’t think there were any 4K 27” given the geometry), and it’s ok but I would really prefer a 5K 27”, those are just more clear although not incredibly so. But they are so expensive to get outside of an iMac. I recently bought my wife a 24” 4K, which has a similar density to the 27” 5K, and her screen looks much better than my 28” 4K.