As I have previously stated on these forums, I don't really tour at this time but hope to get back onto the long distance roads in the next year or two. However, when I was touring in the mid 90's for about six years of rather intense (my friends would say obsessed!) riding, a 1994 Cannondale T700 was essentailly the only bike I rode. The gearing that I had on this bike, after some tweaking) was:
44/34/20 chainrings and a 11-28 cassette.
It was great for touring in the mountains of BC, Alberta, Montana, Idaho and Washington. I'm sure the low gearing (.71 ratio) helped keep me injury free during that time period. And on the other end, I did a lot of no-load training on that bicycle including a few 200 and 300km brevets. The high end was fine for my style of riding which is by no means timid.
My recommendation - use the lowest, low gearing possible for touring.