I keep my code below the 80 column mark, as is common. For me, the reason I like the more narrow Iosevka is because it lets me have more split buffers open on the same monitor. With Iosevka I can have 3 splits with a little over 80 columns each, other fonts only let me have two. I never noticed a decrease in readability but I've been using Iosevka for a very long time now, perhaps it's time to try out a wider font and see if it's worth it.