Practice from 20mph. It's safer and uses the exact same reflexes and movements.
I do plenty of hard stops at 20 MPH and 35-40 MPH, mostly as practice. When I do, the strange, 1.5-2 times/second, braking force pulsation does not occur. It seems to occur only at the higher speeds, above 40 MPH.
As for a stop from slower speed using the same reflexes and movements, I respectfully disagree. At higher speeds, I am responding to things happening on a freeway, which virtually never involves something getting into my path at low velocity relative to mine. Events take longer to develop, and reflex is less important than mental engagement and a sense of trajectories and where the open escape routes will be. At arterial speeds, the quick, full stop is much more critical, and the reflex to get to full braking quickly is crucial. Before encountering this pulsating effect I opened this thread with, I would have agreed about "the exact same movements". But those pulsations are quite dramatic at high speed only when I approach as hard a stop as I can routinely do smoothly at lower speeds. So I end up modulating the brake pressure to keep that strange effect from being alarmingly severe, (a different movement). At lower speeds, I practice hard braking at the force which engages the ABS sometimes, and sometimes at a force just below that (traction) threshold. At the higher speeds, I have not engaged the ABS but once when necessity demanded. As I approach that same force during my 60+ MPH practice stops, that shimmying is enough to make me want to ease up.
My concern is really a safety concern. I want to be able to confidently approach either the ABS threshold or the "stopee" limit, from freeway speeds should that suddenly be necessary. I have slowly increased braking force during these practice maneuvers to be sure that I can recognize when the back wheel starts to lift, under conditions where there is nothing I'm about to hit in front of me. That way, I think I have a better chance of executing a maximum stop when it really counts.