The main difference I notice between a 40 and a 46 on trainers is the extra pull for takeoffs with the larger engine. This helps if the grass is getting a bit tall on grass runways. Hit the throttle on a trainer and it is designed to start climbing. With a 46 you climb faster. Once you have gained enough height to fly around you nrmally throttle down to half or a bit lower. Basic trainer info: Trainers will fly level at about 1/2 throttle, climb at higher settings and decend at lower settings. At this throttle setting there isn't much difference speed wise between the 2 engines. If you spend most of your flight time flying at 1/2 throttle or so then you can easily get in your 10 minute flight. [8D]