Theoretically a higher pitch prop one a clean airplane would go faster. but a lower pitch prop on a draggy aircraft could be more efficient. If you don't have the thrust, power, and drag plot of the aircraft and prop you don't know.
I am going by prop efficiency Thrust HP over Brake HP. Even on a draggy plane if you limit RPM such as by increasing pitch to prevent overspeed or with redline limits on full scale, then the higher pitch will have the most thrust ergo it will have more thrust thus more thrust HP. Even on a draggy plane like say a Cessna 172 the higher pitched slightly smaller diameter cruise prop will result in higher speed (well by a few knots anyway) with the same fuel used. So either way both fuel and prop efficiency is attained with a smaller higher pitched prop. However the larger lower pitched prop may be more effective for aerobatics. People confuse effective with efficiency. Obviously when you are cutting circles in the sky with a model airplane burning nitro fuel, efficiency is not anywhere near your objective. So forget about using the most efficient prop.