I have 4 of the nylon gear versions in a Queque Yak. They are fast, and strong... The Yak was crashed, fixed, crashed, fixed, crashed, fixed... etc... (no fault of the servos..!!!!)... I'm kind of using the airframe for a test platform for the servos, and MVVS engine... I would not hesitate using the blue bird servos in 40 or 60 size models... not sure about anything bigger.. I'll keep updating on the servos... I have to fix the Yak tonight... crashed it Wednesday, when both main wheels came off in flight.... I forgot to tighten the collars...