I spent a while with a 27" 4K monitor. It looked nice in HiDPI modes on my Mac, but I didn't get that much usable screen real estate (I was running it about 1440p). When the pandemic hit and I started working from home every day, I upgraded to a 43" 4k display. I now have the equivalent of 4x 21.5" 1080p displays, which is far more usable than 1x 1440p, even if it doesn't look quite as nice.