Two kiters have had peak speed of over 60knots and several at over 58knots: http://www.gps-kitesurfing.com/default.aspx?mnu=rankings&Year=-&Tab=0&Gender=0&WeightClass=0&AgeClass=0&SpeedType=9 So it is possible, however, the right conditions to sustain this for 500m are hard to find. Yes more efficie...