You really need to begin by propping for "max of max at max" with the new motor, once through the break-in period.
Propping for "Max of Max at Max" means you can turn the maximum of the Maximum range at maximum load. The Max RPM range for the 90 Etec is 4500-5500 rpms. Since the Maximum load of that hull is 1508 lbs including the motor, "Max of Max at Max" means you want to be able to turn 5500 rpms with 1200 lbs of people and gear in the boat.
If you prop it so that it just turns, say 5000 rpms running light with only one person, when you load it up, you might be really bogging the motor, and seriously shorten your motor life. Since, like the Optimax, the Etec has over-rev protection, over-revving really isn't an issue when running light. A good operator won't over-rev anyway.
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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