I bought the Honda 9.9 a year or so ago. An acquaintance advised me to
not by the high thrust model, but to buy the high thrust prop only.
(Maybe Honda calls it Power Thrust) By doing so I saved about $75 as I
recall. The only difference? I didn't get the "Power Thrust" decal on
the cowling. And I'm ahead by one standard prop which is my spare.

Maybe Yamaha's marketing of the bigger prop is as silly as Honda's?
Dale