I've climbed a mountain pass and struggled. I kept wishing for a lower gear and I didn't have one. I've also ridden on level roads with a tailwind and wished I had a higher gear. The first situation is much more serious. I'd go for low on a tourer every time. It's hard to imagine having too low of a range, but I can certainly imagine not having low enough. (My knees can still feel it.) Go low.