Prop for 20 Honda kicker

[Alasgun]

Perusing the prop threads in this forum, I find nothing specifically dealing with my question.
Long story short, BF20 Honda is propped 9 1/4X10 and I am wondering how others are pushing the 25 footers along. First criteria is get home motor so power would be my first consideration, yes I troll with it too but will take what I get there.
The current set up pushes the boat to 4.5 knts before it shudders bad and I believe a lot of slippage is going on. Let of the throttle and it smoothes out but 4.5 seems to be top end?
What think you?
Mike