my axes feed rates are the same (max of 13ipm). Unfortunately, exact stop mode is useless to me for what/how I cut. if I have to run in exact stop mode then I will have to switch to different software or stop using the helical interpolation routines (latter probably the better option).
I'd seen this before on a much older version of mach, and it went away when I upgraded to 3.039, but this is the first time I'd seen it here. it is not picking one of the other axes feedrates, it is quite literally instantaneously jumping (or trying to) between the start and end Z. it is trying to move the Z faster than mach can even pulse at (25khz, 32k steps per inch).