Paul:
I am somewhat in the same position that you are .. except that I have examined closely my particular needs. I need to power a Mercury Air 270 inflatable. For that I have chosen (finally) a 6 HP Tohatsu/Nissan/Mercury. When not in use on the inflatable, I want to use it on my 22 Cruiser as a kicker, for emergencies only. It is not the most efficient motor choice, but it "beats paddling home". I have been agonizing over which motor is best for my situation. The 6 in a short shaft is perfect for the inflatable, but marginal for the C Dory. Some would argue that the short shaft should not be used on the 20" transom of the C-Dory. Much discussion with Les establishes that I can make the 15" shaft work for both. More to come on another thread. The inflatable will handle a motor up to 10 HP and 86 lbs. A motor of this weight would be too heavy for me to lift and put on/off the C Dory. The 6 hp Tohatsu/Nissan/Mercury weighs 55 lbs, the same as a 5 hp. Still a little heavy, but .... A 4 hp weighs 57 lbs, so I chose the most hp for weight. An 8 and 9.8 hp motor jumps the weight to 81.5 lbs, too much to handle on/off from inflatable to C Dory, but better suited for a kicker.
From all the reading and discussions, not from my personal use, a 9.8 hp motor is an ideal kicker motor on a 22 ... if that is its intended use. Left on the transom or motor mount. But if dual use is your intent, like mine, it is too much for one application - the inflatable.
Just my 2 cents.
John
Swee Pea