Something to consider when considering gear composition, is the size of the control surfaces they'll be attached to? Especially on light weight later model scale/sport planes, and no doubt on anything that might be considered 3D capable! Even without considering the extra beating the gas engine is going to hand them, flutter can often rear it's ugly head, even just momentarily, like when you inadvertently forget to pull the power on a down line? I would ask you to consider flutter resistance when selecting your servos? Obviously not a factor on a moderately powered Cub, but surely a factor on an Extra - even a 15-20cc sized Extra? Flutter, even for just a second, can wipe out gear sets in a heartbeat. With nothing available to hold the flying surface steady any longer, the flutter can continue (possibly worsening) as the plane slows, and you could easily loose that control surface, or worse, the entire plane. IMHO, metal gears are your friend here. They're MUCH more resistant to this kind of thing? Extra cost easy to justify. That's me though, FWIW. -Al