Dean,
When considering Davies' comments concerning Vdf and Mdf you need to remember that he was talking about (and flying in) the days before flight simulators. In order to be prepared to deal with overspeeds caused by upsets, pilots had to practice flying at those speeds. They (presumably) did this with no passengers on board! Once qualified current-day line pilots are unlikely to get to do any non-revenue practice flying, let alone be permitted to practice flying above Vmo/Mmo.