Still felt good for the group ride on the 2nd day, 57 miles including the ride over to the start and back - almost wanted to keep exploring afterwards but once I stopped how worn out i was caught up with me. Just caught a ride for the trip back home as planned - kind of wish I could find a good cycling route so I could make a loop of it, but there don't seem to be good choices.
Discovered completely by chance that one of the panniers can haul sixpacks of two local brews the few miles back from the store. That had not been a design goal, but yes, it might have been a thought when I put one back on Saturday morning for the group ride.
Alas when empty they can brush against the spokes, need to work on some additional straps (maybe elastic or velcro) to get them to fold to the outside in that case.