In the max rpm to 85% max rpm range their data doesn't seem to show any worying increase in maximum pressure.
The test stand data given out by Atkinson, Braly & Deakin at the Advanced Pilot Seminar I attended in Ada, Oklahoma showed a 7% increase (approx) in peak ICP when reducing from 2700 rpm to 2500 rpm at WOT/Full Rich. That certainly could be a worrying increase if the detonation margin has already been reduced by other factors!
Even so, they agree it should be SOP for good-neighbour reasons!