btw,
12,000rpm at 6" pitch -> 68mph
12,000rpm at 5" pitch -> 57mph

An LT-40 is no where near stall at 57mph, so you certainly don't need the extra lift that 11mph might give you, but 11mph could be that extra split second between crashing or not

(ob disclaimer, airspeed based on pitch and rpm are ballpark guesses only. Real life is way more complicated)