My advice would be; go with the 9.9. I had one on my 17' Fiberform that I had years ago, and it worked pretty good. I used 2 gas tanks with it. One was 100 to 1 premix for trolling, which would keep it from loading up. The other was my main outboard's auxilliary tank, which was 50 to 1, in case I needed the kicker at full throttle. The extra power of the 9.9 got me out of a couple of tight spots, when the big motor conked, and it idled down to perfect trolling speeds.