Pe Reivers is right about that the a high pitch prop will take more load airborne at climb-out than static. However, when the plane get high airspeed e.g. in a dive, the load decreases and RPM increases. The reason is that in the center of the high pitch prop, angle of attack is above 18 degr. hence, that disc area is stalled static.

As the airspeed increases, effective angle of attack decreases and the prop is not stalled anymore, even i center. (the efficiency of the frop increases). The load on the engine will increase as long as the efficiency of the prop is increasing. At some point, the speed of the airplane exceeds the max efficiency of the prop. Further increase in airspeed from this point, the load on the engine will decrease.

This is why 3,75 is the lowest pitch you'll get on a prop, this is max pitch you can have static without ANY part of the prop beeing stalled at static speed.