I think the delay comes from Mach having to see the next rate/spindle speed. In other words, if Mach sees a feed rate of 100 IPM and is running at 100 IPM. You adjust the rate, it doesn't change until it sees another F value. I have not had time to test as I would like. I'm not sure if the number of lines look ahead affects this. In any case, I would want my number of lines look ahead as high as possible.
Brett