Why not just let the aircraft fly the speed that they want. After all, they pay the fuel bill and if their Company wish to exercise control re. fuel burn then that is their business. ATC seem to be interfering far to much with the speed that aircraft fly at with only scant knowledge of what is or isn't an appropriate speed and then after lots of vectoring all over the sky ending up in one of the TMA holds for 15 minutes. Tell the plane how long the likely holding is as early as possible and then let the pilots work out their best speed to try to achieve minimum holding.