to answer the mileage question, I get around 50 on either engine. I'm past being ricky roadracer, I ride at a respectable pace, but I still smell the roses.
you want power? get an oilhead or a k-bike.
if you want a good touring bike that will take you and yours all over the place and aren't a speed demon, that r80 will work just fine. as mentioned above, do some suspension upgrades and put 100k on that thing!