Thanks Cosmo,
You're probably correct about my over estimation, it would be something like 40kt increase from 0.82. However, we know how astonishingly quickly things can unravel at 40,000 once problems occur.
Thanks also for the report, the FDM recorded max was an astonishing 429kts! This was quoted as Mach 0.719. I guessing the FDM sampling rate is the reason why the pilot noted a higher speed. Looking at this
"Diving" Into A320 Diving Speeds the A320 Vd is 381kts, which must be similar to the B737!
Check you this
video of the A380 flutter tests (also at the end of the linked blog)