Bottom pain will cost you about 8-10% in top speed. A boat that runs 45 with a clean gel-coat hull will drop down to about 41 with most ablative bottom paints. Painted hulls also ride lower at the bow at a given trim angle because of paint-induced drag.
Moose is right: weigh your boat. Your Armstrong bracket is NOT a full flotation bracket, i.e.; it does not support the full weight of your motor. It mitigates the weight somewhat, at best.
With that bracket, you REALLY should be using a 4-blade prop to provide stern lift and maneuverability. And whether using a 3-blade or a 4-blade, remember to "prop for Max of Max at Max"
That means to prop so that you can achieve the MAXimum end of your MAXimum recommended RPM range when the boat is at MAXimum loading.
You may sacrifice some top speed, and be able to go above the maximum rpm range when lightly loaded, but you put a whole heck of a lot less strain on your motor that way. (And just because you can exceed the maximum recommended rpm, don't. Your motor will thank you for that, too.)
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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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