what it comes down to here is how much weight you put on the bike, combined with how steep hills you will hit. As for your concern about falling over, unloaded its one thing, but throw on 40lbs of stuff (a very easy amount to have with camping gear, cooking stuff etc) and you will be working really hard with a lot of power going into your pedalling, even at 6kph. I could take up hills right here in Montreal that you might find pretty darn hard with 25 gear inches and a full load. I've toured with my mtn bike, with about 25-30lbs on the bike, and in very steep hills Ive found myself looking for a lower gear than its lowest 19.5, but it was ok (again, put another 15 or 20lbs on a bike in the steep situations Ive been in and you would want lower).

all this blah blah will mean nothing until you load your bike up and hit some really steep hills so you can see what works and what doesnt. One thing to think about, people often poo-poo really low tourer gearing, but when you have a bunch of stuff on a bike, you aint going fast the vast majority of the time, and going up hills you'll be going pretty slow.

the change to a smaller granny is the easiest, cheapest change. Ive changed the 30 granny to a 26 without any need to do anything to the front derailleur-this will give you about a 21.5 g.i. which is a pretty good low that Ive used a lot (but Ive kept my load to about 40lbs, and Im a light guy.....more weight will be harder)