This is not neccesarily true--one can program a servo to work at a certain speed. For example, if you wanted a servo to move to the position represented by 1.0 from the position represented by -1.0. You could do this by
- Setting the servo to 1.0
- Using a loop to set the servo to -0.9, then -0.8, etc
If you're using the second method, you should be able to move your servos faster by increasing the amount they move per cycle.
Another thing to keep in mind is that if the you're getting a low frame rate due to processing delay, it's pretty easy for the target to leave the frame, since the system can't update the servos. Something you might want to try is predictive tracking--say, if the 10 previous frames have involved the target moving in a given direction, you can make an assumption and move your camera before processing based on an estimation of the movement speed.