Prop size and number of blade and pitch matter too
First off I love my Tohatsu 9.8 4 stroke. I suggest you get the highest HP you can in the weight range you are looking at. The Tohatsu is supper quiet is excellent on fuel and weighs in at 81 lbs. It also has at least 4 different props available. The standard prop (8.5 d x 8 pitch 3 - blade) is actually a good compromise for up and down river work of med weight raft or cat. The 3- blade 10 pitch prop they make works great downriver with a loaded cat. My favorite prop for pulling multiple boats though is there 4- blade prop for heavy loads, which is also there smallest diameter prop at just under 8".