I just crossed PA with full camping and cooking gear. My stock Surly LHT has a 26x34 low gear. 32c Conti Contacts. I used my granny plenty of times on very steep hills. Got down to between 3.5 and 4 mph without stability problems. There were times I wished I had a 24t chain ring. Something I have been meaning to switch to but keep putting it off.

Crossing the country many years ago I had MTB gearing. Lowest gear inch was somewhere aroud 17.5. I never regretted it as I was carrying a lot of heavy camera equipment.