When I use an IDE, I use a proportional font. (Gasp! Shock! Heresy! Blasphemy! A witch!)
The 80-column constraint becomes irrelevant, except if you have to work on a team. And the team imposes a coding standard of 80-columns. (Or 100, or 120, or whatever.)
These days I expect my IDE to handle soft line wrapping properly.
I had started using proportional fonts a long time ago, after reading Bjarne Stroustrup's C++ book where he had used a proportional font for all the code examples (back when most programming language books had all their code examples in a monospaced font).
My favorite proportional font for programming is Input font, by David Jonathan Ross released by Font Bureau. It's free, and has some customization options to tweak it to one's preferences. input.fontbureau.com/
There is a surprising shortage of good proportional fonts suitable for programming. I've taken a few popular fonts, and tweaked them using Fontographer, to make them suitable for programming for me (I never released them into the wild, for obvious reasons). But I'm glad to have found Input, which I like better than all my one-off attempts.
When I'm using Vim (which is often), which is not proportional font friendly, I use Fira Code, by Nikita Prokopov adapted from Mozilla Fira. github.com/tonsky/FiraCode
Historical trivia: C used to have a character line limit of 509 characters.
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