Flatiron
I once flew a Vulcan Mk1 to the corner of the flight test envelope which was 415Kts, 0.98 IMN and 3.0g with weapon bay door open. Elevators were close to max in a spiral dive aiming to have 415Kts coincide with 0.98IMN. Lost control with nose down pitch and full up elevators. Recovered control in denser air following power off and speed brakes following a supersonic excursion.
Subsequently learned that ribs in the nose cone were the weakest part of the airframe under high Q (IAS) which explained a pop open of the oxygen filler access during the above. Rear bulkhead of the weapon bay was deformed. We must have been a smidgen away from the same fate as VX770.
VX770 could be expected to go out to around 415 Kts without a problem except for possible inadequate quality of the reskinning of portion of a wing. Also there may have been a restricted performance envelope on VX770.
I heartell that VX770 exceeded 415Kts by a substantial margin.