Not sure if your real question was answered correctly. I found a system variable in $MCR_GRP[1], labeled $OTF_SPEED, that monitor the "On-The-Fly" speed in mm/sec.
I'm going to write a BG program to write that speed to a register for all of our robots, just so that I know. Could use it to find the average speed your robots are running at as a way to prove to the big guy's up top that you're making a measurable process improvement.