OK so at 28,800 steps per unit (inch) you will get a max possible axis speed of the following,
25KHz = 52.08 IPM
35KHz = 72.92 IPM
45KHz = 93.75 IPM
60KHz = 125 IPM
65KHz = 135.42 IPM
75KHz = 156.25 IPM
100KHz = 208.33 IPM
now whether you can achieve these speeds will depend on many factors such as your motors, drives, power supply and computer.
Hood