FLAPHappy
You can usually get all the throttle response you need out of even the most basic servo . What really maters is the geometry of the linkage to get the most out of speed and position accuracy. Any servo with more than 50 in oz.of torque will usually surfice. If you have a computer radio with the ability to set a throttle curve and servo speed along with good mechanical geometry can make things easier on you . But the real key to good throttle response is a properly tuned engine . A poor tune and all the throttle servo speed in the world wont save you when the engine stalls.