servos will do just fine,ST 51 if you use the stock muffler it may be a little nose heavy?
i am a firm believer in using what you have.i have a old Italian made ST51 and it runs great,at lease the last time i ran it,it's on a trainer and still have both.
the EF Chinn Yak is one wicked 3d monster,you love it,but it is fragile.