My current setup is 4x22" at 1050x1620. I originally started with two displays, but kept adding over years. I think each display increases productivity by half

My current setup is 4x22" at 1050x1620. I originally started with two displays, but kept adding over years. I think each display increases productivity by half of previous (2nd display adds 50%, 3th adds 25% and 4th 12.5%). My secondary screens are slightly damaged (dead pixels, scratches...) so they cost peanuts. The real limit is electricity bill. Also with such large setup you need good light balance. I always use inverse color scheme (light on dark background). For example I even filter web page colors. I am upgrading because my laptop and phone has retina display and I love it. Also LED displays should have lower energy consumption compared to my ancient displays.