The facts:
9'X5' inflatable with inflatable keel and hard floor.
5hp 4 stroke engine.
7 1/2 X 7 3 blade prop.

Here's what's happening:
Engine runs smooth as silk.
At about 1/2 throttle GPS measures 4 1/2 MPH
At full throttle GPS measures a little over 5MPH
There is no noticeable change in pitch or DB between 1/2 and full throttle.
Engine doesn't seem to be bogging down.
Speed increase between 1/2 and full throttle is gradual even though
throttle is advanced quickly.
Boat bottom is clean.
Prop is in excellent shape.

Questions:
Is this normal?
Should I try a lower pitched prop?
Do I need more Horsepower?
What do you think?