I have had models that went from a tiger to a *****cat on landing with as slight a change as a 11X6 to an 11X5. It's like downshifting. Lowering the pitch is like going to a lower gear. It's easer to park in first gear at 10 mph (12x4) than in third at 50 mph (10x6). Lower pitch gives better low end torque but less speed.

When you change the pitch 1" change the diameter in the opposite direction. (i.e. swap a 10 X 6 for an 11 x 5).

And try APC or ProZinger. My two favorites.