So update...

I got the Marathon HS420's in 37-622 and they measure exactly 37mm when inflated

Though I think I immediately regretted this when I put them on the bike.

They look too thin, and ended up being thinner than the 37's I had on there. With the cheap suspension fork they look comically narrow.

I'm wondering if I should have gone with the 40mm tires, now that we've removed fenders from the equation.

They are slightly heavier, but would they ride better? Be slower? Would I even notice? I am overthinking this?