A higher HP would probably be better, as stated above but, there seems to be many Pro kicker 9.9 HP high thrust/high output options out there that what would probably work as well. Probably comes to initial cost (if buying new), operating costs, thrust available, etc. They would need to dig into weeds to flush all that out to see what would work functionally and what would be the most efficient from an operational and cost standpoint. If both motors can maintain 5 hp consistently (9.9 HO and a 15/20 HP standard), does the 20 hp at 1/2 throttle burn less than the 9.9 HO at 3/4 throttle? What is the weight difference, cost difference, etc.?