Don't know about Fat Franks, but after going through some unconfortable 26x1.5 slicks in the past, including Vittoria Randonneurs, I put 26x2.35 Schwalbe Big Apples yesterday on my MTB and went for a 50Km ride, half of it on cobblestones and the rest on cracked pavement with some sandy paths thrown in.
They're a little heavy (800g* or so for the 2.35), but once up to speed they've got very low rolling resistance even at somewhat medium pressure, and are very confortable. Grip was not a problem, but the ground was dry. I don't think punctures will be a problem, but I'm using kevlar liners, just in case.
If the roads you're travelling aren't that bad maybe you could go with the lighter, higher pressure 26x2.0 Big Apple.

*corrected from 600g, after checking the Schwalbe website (if it can be trusted)