I've only used short shafts, long woud do a better job of keeping the prop in the water, and the head out of it. But they're harder to find, heavier and a biat harder to get completely clear of the water when sailing. I probably used one tank of gas(1 quart, internal) for the whole season., as I never had far to go to get to wind, or back home. I'd counsel against bigger motors, weight is your enemy on a small cat.

dave