You might be interested in some early data from my bathtub?
I have got a test boat together - see it at
http://modelboats.hobby-site.com/RAFPics1.html .
I have just given it a first run with a brushless. The figures are:
9v dry Batteries (9.33v off-load) - Fine pitch propeller thrust - 66gm
Coarse pitch propeller thrust - 125gm
2 cell lipo battery 20C (7.92v off-load) Fine pitch propeller thrust - 427gm
Coarse pitch propeller thrust - 395gm
I interpret this to mean that the brushless motor can soak up a lot of energy if it's available. With the dry batteries the motor was limited by the amps the dry battery could put out, which was low (AAs). So the prop could only spin up to a certain fixed speed, and at one speed, a coarse pitch prop will provide more thrust than a fine one.
With the Lipo, the motor could have as much energy as it wanted, and it was limited by the drag from the propeller. The high drag of the coarse prop kept the speed down, and the extra speed the fine prop provided actually produced a noticible increase in thrust.
Of course, someone else may know different.....