This is a tiller steering OB, right ? Before playing with prop pitches wildly you should invest time in water experimentation to get the max out of that combo, which by the way is ?
With deck weight evenly distributed trim OB for combo to run parallel to water level at plane, when that happens will have AV plate and prop shaft riding parallel too. That's where the prop achieves the best thrust as all blades bites even at same angle of attack.
A must check at which lower leg is water flow passing at speed. Tohatsu lower legs loves for water flow to skim right under small upper water deflector plate. If in need to rise, chop transom down it's other story, at least need to determine so. If at wot OB sits to high prop will spin with less water bed, will achieve slight more wot rpm with less prop thrust.
Have not stated when OB over revved how loaded combo was, did the rev limiter ever kicked in or not ? sometimes you need just a half pitch to be at the max wot range as loaded and rev limiter staying home. Can send that 11 to a prop shop and have it repitched to a 11.5.
Having 10 and 11 props should make a wot test say solo boating and as currently loaded and report max achieved rpm with both props to check wot rpm gain or loss difference between both pitches, .
Bottomline, it's near impossible to dial best prop performer for your application on first try, usully on second if not on third. Took me testing 3 / 9, 8.5 and 9 pitch props to dial best prop performer as fixed loaded. The 8.5 did the final trick having already a previous OB height optimization.. OB's powering light applications could over rev depending on the pitch size factory delivered.
Happy Boating