For something like the LT 40 I would go with less pitch and keep the diameter up.You well have better thrust and lets face it a LT40 is not designed for max speed.Try a 11x5 APC or a 11.5x 5 Bolly clubman.It well still be fast but it well also jump into the air on takeoff and vertical way better.Vertical performance well far exceed a 10-6 or 10-7.Just my 2 cents.Dennis