@zonoma: Strange. The minibus achieves around 1000ft/3NM descent easily, if the speed (whatever speed!) is held constant.
The extra 12 miles, to make a same level restriction, should have given the trailing aircraft another 4000 ft of geometrical room. Thus with 8000 feet of "energy advantage" it is hard to imagine one would need 300+ kts to match a profile of other jet (any) descending at 250 IAS.