Well, that's awfully close to saying I'm incapable of writing down my observations correctly. What I wrote is what I'm seeing.
One thing to remember is that I'm running the Estlcam machine controller, not GRBL. They are different in many ways, and I'm trying to get some help from Christian regarding Estlcam, not GRBL.
Issuing your second sequence of commands (adjusted for metric)
G0 X200 F8000
G1 X-200 F2000
results in a rapid move to the right, followed by a slow move to the left, to the right, and to the left again.
And that IS 100% accurate.