If you are happy with your current overall performance than the same pitch and diameter should be very similar. You should have a bit more hole-shot (more bite from more blades), top end may be down slightly (more drag from more blades). Typically when going from 3 blades to 4 I suggest going up 1" in pitch. For me, this has resulted in better hole shot, better control at low speeds, and about the same top end/RPM.
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Walt B
"Debt-Charged"Black '07 H210SS6.2L Bravo One turning a 21P HIFive
Wakeboard Tower with Perfect Pass Stargazer version
Missouri River; Kansas City, Mo.