Charles,
The aim is to have fast variation of the thrust, in sharp corners. Throttle adjustments are slow, because of the inertia of the propeller.
Pitch variation is quick, because servos are fast, and the inertia is helpful to keep the revs constant (the constant sound pleases the judges…).
Tim,
How Igor uses the acceleration sensor signal I do not know. I use it simply to keep the line pull constant.
The response is much faster. As you mentioned, the frame rate should be as high as possible, I use 125 Hz. Futaba analog servos work fine at this rate. If you are interested, I could post a Castle data log.
All the best,
Wolfgang