I've had 40' 4k for about 3 years, it's awesome. I had to mess around with setup because larger screen changed way I worked with stuff. But man, i can see from column A to EP and around 400 pdf pages (really small text).

http://imgur.com/a/kPRzq ^ eventually what i settled on, use 1920 as primary and if working on something would go on bigger.

23 Left Dell (emails, windows I'm not ready to close) 40 seiki ( excel, factset/bloomberg, chrome) 23 center hp (word, typing emails, reports) 23 right hp (xplorer2, network,file related)