would this difference be less if I ran a higher frequency?
The selected Kernel Speed defines how many pulses you want the computer to output when using Mach3.
The Driver Test, when run, will confirm that the selected Kernel Speed can be used in harmony with Windows since Mach is sharing time with the operating system. Changing the Kernel Speed will change the graph in tuning increasing or decreasing the max allowable velocity the software will use. There is no advantage to using a higher Kernel speed than necessary.
The computer output ( number of available pulse instructions to the drive ) can restrict
the velocity, the steps per unit input is calculated and is composed of the axis components, the drive may be limited to how many pulses it can send to the motors,how fast something can accelerate to a velocity is dependant on the axis systems ability to provide adequate torque at some rate to address the systems inertia. All this is inter-related.
Using a higher Kernel speed does not mean your machine has the capability to achieve the higher velocity that the software is using.
I would be interested in your reply to Hood's question. Are you near the max velocity that your machine can run at for 30ipm?
RICH