The servo controller module inside the E665 control unit can be tuned to move the PI-726 piezo objective holder as fast as possible. 6ms should be achievable for 10µm steps with the Zeiss 20x objective.
Unplug
Take the lid off (6 screws side and rear)
Plug back in
Identify servo module (see manual)
Identify P1-P4 and P6 potentiometers
Choose a step size on the large end of what you will use for a single step (we did 10µm)
Have Igor give a whole load of pulses at that step size
Change P3 and P2 to make it faster (these are integration time and gain of feedback loop)
If you can't get any faster then change P1 Slew rate limiter to allow faster movement
Try to get something as square as possible and be prepared to have a very slight overshoot at the start of the step (100-200nm may well be irrelevant)
Adjust P6 (it may need quite a few turns) to get step size to be exactly 10µm again.