You should be able to get up to at least 7-9 mph. I have a Pelican Bayou 160 scanoe (16'3" and 40" bottom) with a Yamaha 2.5 4 stroke and I can reach those speeds (GPS tested) with about 600lbs of passengers and cargo, not including the boat itself @115 lbs. Considering that a scanoe is a full displacement hull (like a barge, never meant to plane) and a jon boat is planing hull (flat bottom boat designed to plane) you should be able to go faster than those speeds. The biggest disadvantage is the 2.5 motor uses an internal fuel tank, which holds a quarter of a gallon of gas and lasts a little over an hour @ WOT. But that means I get about 30-40 mpg @ WOT. It is very cheap to operate all day, just hard to refuel when the waves get bigger.
