In a discussion on /r/coding, people once again debated the merits of the old 80 character per line rule. My usual argument is that we want to put several code windows next to each other, so yes, we do want to limit things to 80 characters. The author of the linked piece mentions this, but I don’t think he makes a persuasive counterargument.
I might have changed my mind as 4K monitors become standard, but then someone in the discussion linked this:
This suggests that you should limit things to 50-100 characters per line for typographical reasons. Now, they’re mostly talking about prose writing there rather than code, but lacking studies otherwise, setting the limit to 80-100 seems sensible no matter how big monitors get.