Our Company SOP is to fly at the FMS generated speed unless there is a good reason not to. However on a short route (eg MAN-LHR) filed at say FL190, The FMS Cruise speed will be high, about 325 KIAS. At Top of Drop the new descent speed can drop to around 275 KIAS resulting in Cream Tea in the seat pocket and controller head-scratching.
So, the MAN flight going through 'BNN25, 150 or below' will be at 275 KIAS whereas the EDI flight, same type etc., will be doing about 310 KIAS. There used to be a memo out a few years ago on the 737 fleet about manually changing the FMS generated DES speed to be the same as the CRZ speed when flying a low-level route, but I don't think this has filtered through to the A320 yet.
Pilotwolf: 30 KTS straight, 20 in the bends. V. accurate speedo on board derived from FMS!