Yep, 27" 4k at 1.5x (plasma) I can have 50/50 or 60/40 with font size 14 and get 110+ characters, not just 80. 60/40 would be for an IDE with a bar or two on the side and still get almost 110 columns in the editor/console comfortably without eye strain. With 144 DPI fonts on plasma (using Hack), fonts seem plenty crisp to me down to size 5.

For screen size, I think there is some screen size that's most comfortable to view, and I want to say that's like ~40% of the human FOV... so, I think a 24" monitor and 15" laptop are most comfortable for me, but 27" might be a bit nicer if you're using it for media as well.

I miss read a bit when replying in the other comment, for 4 side-by-side 80 column windows, you'd need to bring the font size to 9, which isn't as comfortable as 14 for me in my side-by-side setup, but then 1.25x is also an option.