A mountain bike triple mated to the cassette or freewheel of choice should give you all the gear range you would ever want or need on a touring bike.

With a modern 11-34 cassette and a 22/32/42 the gear range is 17 to 104 gear inches on a 622:38 wheel and is 17 to 98 on a 26 by 1.9... the low gear does not change as much when you change wheel sizes and anything over 100 gear inches on a touring bike is going to be pretty much useless unless you like descending at 80kmh.

With the mtb triple, changing the 42 to a 44 on the 26 inch wheel matches the top gear you would get on a road wheel.

The compact triple I have on my Cascade can run a 20 tooth granny so I mated that with a 12-32 7 speed which gives me 16 gear inches, the 44:12 gives me 95 gear inches up top and if I spin that out I'll be doing 55-60 kmh and did hit 50kmh on the flats this past weekend.