I run 13/48 and find it great offroad. Can sit on a 100, probably revs a whisker higher than I would like to sit on that all day. But its really not too bad.
14/48 for longer higway trips?
I ride my bike offroad a couple of times a month and then commute every day, also have a second set of wheels (48T on both). Dunlop 605 on the road, front and rear and Michelin AC 10's front and rear offroad. Although this week I've been on the AC10's all week as I didn't have time to change them and heading offroad again this Sat.
You'll need a new (longer) chain I'm guessing with a 48T rear.
13/44 is slightly down geared but I think you would like the steep climb power of the 13/48. It's what most people run. You can still do 65mph on road with it.