Hello,
If you really are controlling the speed of the motor and not the position then there shouldn't need to be any difference, if the speed never reaches the setpoint you need to increase the I-gain. That should make it come closer.

If you use the "moving target" aproach, ie. you are in reallity controlling position then, as long as the motor is moving, there will always be a discrepency between the target and actual position, called following error. The speed however, should match the command , otherwise the following error would just grow larger and larger.

/Henrik.