Rapid speeds

How can i find rapid speeds of machine ?
Is there an automated script that measures displacement/time to calculate rapid speed ?
Also how can measure max rpm of spindle with encoder installed ?

In both cases, if the encoder is scaled correctly, the encoder velocity will read
machine units per second for linear axis and revolutions per second for spindles.
(there's also revolutions/distance per minute encoder velocity pin)

So if you can command a maximum speed (10V on an analog system)
you can measure the velocity/rpm with the encoder feedback.

For linear axis you will have disconnect the motor from the ballscrew to do this test
also the maximum actual speed will be 10-20% less than the speed at 10V
because the PID loop needs some overhead.