The 9650 is a mini digital servo with plastic gears and 4 mounting screws as opposed to the micro servos 2 mounting screws. It is also used by some for elevator servos when running a 2 servo leevator setup. This means its light, fast, strong, resistant to vibration and has great centering. Its actually a bit overkill for throttle use but it is the best, in my opinion.

Jayjay