As quoted above, Quique does recommend the use of a fast, high torque, non-digital servos. Specifically, the 4721 and 4735.

I've used the 4721 on several airplanes and it has worked very well for me.

When going to higher voltage, non-regulated systems, such as the A123 batteries, I have to swap this throttle servo with a Hitec servo capable of taking the voltage. Currently experimenting with the HS -5645, which is digital.