I was involved with another study in Europe involving airports, airlines and air traffic providers. One of the issues I remember was delays caused by choke points at particularly busy airway intersections/sectors, SPY near Amsterdam and TRA near Zurich being good examples. If the flow rates were predicted to be exceeded, this resulted in restrictions being issued with Eurocontrol delaying departures. If you could route the traffic avoiding such points there would seem to be plenty of potential for improvement.