First off.. BVM recommends the 3301 on the elevators, not the 3421 if I remember correctly. Whether you choose to change servos is entirely up to you. There have been literally thousands of flights on the recommended servos without issue. The real advantage a metal geared servo gives you on elevator is resistance to gear breakage from a hard landing. The elevators have some weight to them, and a hard landing can induce a shock load on a nylon gear train that can damage them. I would suggest using 9411's or 8417's on the rudder. The 8417 is overkill.. no question.. but it's MUCH better suited to handling a gyro than any other non-heli tailrotor servo. As for the gyro, I would not suggest using the 410. You cannot shut off the gain. Get yourself a JR 460 or 500 (new JR model gyro).