I agree that idle is higher in the upper cruise levels than lower down. However, one would think that that solves the problem originally posted in this thread! Right? No longer spool up time because of the higher idle?
Anyway, airmanship, dare I say the word, dictates that you do not fully close the thrust levers when faced with a transient overspeed condition. That would be a gross overreaction (and not SOP on top).