Guys,, do as Bill suggested.. Use a 'normal' servo...
I tryed a FUT3004 and I tryed HS225 and I tryed HS525...
The 3004 were the best.. I do use the 225 when I need a
smaller servo as limited by space.. I ended going back to
the 3004 servos on the test plane..

A faster the servo usually will cause oscillation, which
is one servo reacting then the other reacting causing the
motors to not sync as quick...
The unit itself has a real fast reacting time so as Bill
said to use a high speed digi servo is useless..

Just make sure the servo end points are set to a
MINIMUM of 100... The more the better.. The larger
the end point number the more preciese the servos
will be..
While trying different things I set a low end point..
I started out with a 40 low side and a 65 high side..
Major oscillation thru out the throttle range.. Then
after talking with Bill on this changed the throttle
linkage so that I would have a larger end point number..
I now have it set at low of 125 and high of 130...
Throttle response is great, sync'n is fantastik all
thru throttle range.. And,, zero oscillation at any
throttle setting even if I jam the stick <which I do often>
(BTW, I use a Futaba 9Cs)
So,, the larger the end point, the more precise the servo,
even a 10$ servo.. So save the good servos for the control
surfaces..