I fly my Rascal 40 with a Saito .50 and standard servos. Is extremely well balanced with plenty of power with a 11x7 Graupner prop. Great plane, coupling of rudder with ailerons makes it very responsive in flight, but turn the coupling off on landing approach or suitable aerobatics as rudder is small but very effective. The LA 40 should be plenty, but it does fly better with the larger diameter prop that the 4 stroke allows.