Thinking about a different prop on my 1850

[belairbrian]

I made another run today on the river.
Had the pitot speedo reading 42 and GPS reading 40 at WOT.
Last run had GPS only showing 39.8.

I may be a bit off as I was standing while under way and I don't see the gauges straight on.

Prop is 14x17
WOT is between 5000 and 5200
140 Johnson v4

I actually would like to back down the top end speed.
I was thinking a 14x15 prop Probably the OEM one.