I spend more time than most trumpeters performing is small group ensembles in the upstairs range, and do not buzz at all. I phwooooooo. I think the ability to play sustained in the upper registers goes beyond whatever vibratory method is used. Don't get me wrong, vibrating is essential, but I find that the cushion of air I have behind that vibration is key. Using that air wisely enhances the vibration and minimizes the force required to keep the vibration going.