Also what's up with those side margins? A little margin is nice (HN's feel reasonable), but the margins on both PMFW and BMFW look like they follow the philosophy of maximizing scrolling and margins to cram a bunch of ads in the margins, only without the ads. One caveat might be that I'm viewing them on a desktop monitor and not on a cellphone.
(Edit: Okay, I should have read TFW. They mention the reason for the line width)
Apparently optimal reading width is approx. 65 characters wide.
There's definitely a sweet spot; I typically have my browser windows at 2/3 width on a 2560px wide monitor. 100% width lines are a chore to read honestly, there's definitely a higher cognitive load.
(Edit: Okay, I should have read TFW. They mention the reason for the line width)