I'm a little confused. From experience, a 2 stroke 150 black max was plenty of power for a 20 Seafari, even seriously overloaded for scuba diving. I don't remember speed very well, but 25 knots at cruise(4000 rpm) sounds right. Much of the time it was too rough to use the power. Loaded light, WOT was in the 40 knot range. Does weight of a modern engine make that much difference?
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