I think it was cross talk.
I made a change in Repetier firmware changing ALWAYS_CHECK_ENDSTOPS from 1 to 0. This means they’re only checked during homing. Of course this is not the solution. Instead I’m going to look at my end stop wire routing, and employ a bit of twisting and perhaps shielding.
I was able to print the part this time with no layer shift. Because I had the idea it wasn’t speed related, I tried pushing things a bit. My printer has steel rack and pinion drive, a very solid mdf frame and powerful steppers for the job. Basically it’s designed to be rigid enough for milling. After trying everything to get rid of the layer shift, I’ve got it super tuned now!
As it turns out, I could go back to all the defaults for acceleration, jerk and print speeds, and print fine. Finally I tried it at a 150% feed rate multiplier, and it printed fine with only a tiny loss in print quality. So travel of 195m/s and print speeds of 90m/s.