The tires are the 37mm Continental Contact tires that came mounted on the bike originally in singlespeed form. Their actual mounted width is 34mm. It looks like I could fit true 38mm tires. I'm running 60psi front/70 rear. I think I'll try about 5psi less in each next time.

While I could ride these roads on a MTB, it would be a very different experience and not what I was after. What I like about this setup is that I can ride paved or unpaved roads efficiently. There are many roads here that start out paved, but the pavement ends and the road continues for miles before the pavement starts again or the road ends at a paved road. The tires need to be rugged and wider than typical road tires, but knobbies or 2" wide tires would be overkill and would detract from the on-road part of the ride, as would flat handlebars. For my preferences, a rugged road bike is the ticket for this, not a MTB.