Indicated airspeed at high altitude
Cheggars
I think what our 737 pilot was getting at is that 300kts indicated at FL270 to FL300 is equivalent to a Mach speed that is higher than the Mmo of the aircraft. There is also a possibility that he is conservative in operating close to that red/black "barbers pole" speed limit on the airspeed indicator.
For my part I am more than happy to oblige in the 777 with Mach .84 initial descent speed and 300 - 320 kts below FL270.
It's the 160 to 4DME that can be the problem.....