I just returned from my first touring trip with a bike (a short test ride). I also used an old Mountain Bike (hardtail with rigid fork) with 46-38-28 crankset and 14-28 freewheel (6-speed), equipped with 40-559 tyres (Maxxis Xenith 26x1.5). That would give around 25 gear inches in lowest gear.

One of the clear conclusions that I drew from this test ride was that for me 25 gear inches on a loaded bike is not low enough. I already have a new transmission and rear wheel for this bike (bought before this test ride, but not yet installed) and it will be 42-32-22 crankset with 11-34 cassette (9-speed).