I would suggest a TT PRO46 myself but if you really want a 4 stroke then get the larger 56. Sure you only need to fly at 1/2 throttle once its up there but you do have to push the plane up to flying speed and if the grass hasn't been cut in a while..... I had a 40FX on my LT40 and was lucky to get up to flying speed in the tall grass. The extra power also helps get out of nasty situations!