I set the throttle linkage by loosening the retaining clamp, pulling the throttle trigger all the way, opening the throttle all the way by hand, and re-tightening the retaining clamp. That way the throttle servo opens the throttle all the way and no further, with no need for a spring to keep the throttle servo from pulling too hard and damaging the linkage.
Servo speed is set at 100% and can't go higher; the power supply is already 6V, and any higher would burn-out the servos.