yes that's true 5 km/h Boost is more stress for the DU then anything else
maybe they mean this errors...? and i can't imagine what means 75,4 km/h ... downhill?!
"...
we have just checked the submitted Shimano STEPS motor DU-E8000.
The drive unit has several sensor deviations as well as a gearbox damage.
According to the detailed evaluation, the drive unit was operated several times at an excessive design speed.
This will result in a loss of warranty...