Why do you feel you need an 11x5 on a LT40?

The lower the pitch the more torque but the less speed and an airplane like the LT40 produces lift with speed. The lift generated off the wing makes it fly, not the engine. The engine just pulls it forward so that the wind over the wings will create the lift to make it fly. Take away that speed and you produce less lift.

An 11x5 will fly it but your not going to benefit from it, at least not on an LT40. It'll just take more rpms to make it fly resulting in more fuel use.