Mike:

Create your calculation matrix around a 60% throttle setting and raise
the pitch figure higher. Instead of selecting a random pitch number
consult the prop manufacturer's indexes to find something at least 9" dia
x 9 or 10. This will result in a higher flight speed and better initial and
midpoint thrust.

Your initial 49 mph at 100% throttle is not going to cut it. You need to
augment the calculator's results to your advantage to achieve not only
more torque and forward speed but you need to lengthen the flight
duration. Your original 100% selection does not provide you any wiggle
room as as margin of safety and effeciency.