Ive had very poor luck with those HD servos. I would hesitate to use them in any model I cared about - or in anything at all actually. They center terribly, use a LOT of power and fail easily.
I would highly recommend you use quality servos. Hyperion, Hitec or Futaba digital servos would be an excellent idea.
Id also use a separate 10 amp BEC or 10 amp regulator with a separate hi capacity rx battery pack - like an A123 or 2 cell lipo pack for example - for receiver power and disable the internal BEC on the Castle if it has one.
Large heavy war birds need extra attention paid to the components you use. They are expensive to crash and dangerous if they get out of control