I'm going to echo Denny here. Go to mounting height before spending too much time with props.
I used to run an '06 90hp Optimax on a 20' Seafari and I eventually got a WOT speed of 36 mph at 6050 rpm running a 4 blade PowerTech OFS 15" pitch. The 90 Opti was actually about 110 hp at the prop. As a SeaCraft dealer back in the early 1980's, I sold a number of new 20' SeaCrafts with only a single 85 hp Johnson on the back, and even one with a single Johnson 70 hp which ran fine with a top end of about 25 mph.
I had to raise my Optimax 90 to where the AV plate was 1 3/4" above the keel before I could get above 32 mph with ANY prop, and most of them wouldn't get me above 30 mph.
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Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.
Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!
Currently without a SeaCraft 
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury
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