The other summer, I ended up riding about 310 km in three days, due to a small error in calculating how many days I had available for the trip.

I carried full self supported touring gear and had a 5,5m long sea kayak on tow. I was going for a combined bike/kayak tour in the Finnish Lake District.
I stopped a lot. Zero problems with the hybrid bike, trailer and the kayak, they all could have easily done more. Me - not so much. I was very happy to finally reach the lakeshore and start paddling. I agree it's all about the motor, but clipless pedals, bar ends and a comfortable riding position help a lot.
--J