Steve,
The rate is set in config>general config and can be changed at your whim. I have found that jog rate of .025" is about the maximum needed and .001" is good for general use. The rates are selected from the tabout screen when in MPG mode and jog is enables. A brain file can also be written to select both the axis and also the rate.
When properly set up the rate is exactly the setup rate.
Cheers,
Kenny