I have a 27"" LED Cinematic display. It has served me will for many, many years. I would like to now add more "real estate." What would make the most sense; getting another 1440p monitor, or getting a 4 0r 5K monitor and size it to 1440p?
More "real estate" means higher than 1440p resolution. You can go 27" again but everything will be smaller... but you'll have more "real estate". If you desire the approx. same size windows which appear with 1440p, etc, you'll need bigger than 27", probably a 32" 4K display.