VC10 figures can be misleading as the indicated mach number overeads by 0.02 - so a quoted speed of 0.925 (the old crew trg limit) is actually 0.905. Limitations imposed in the late nineties reduced the true MNo to below M0.85 and also ended the practice of operating up to the MNe limit (0.92 true) for "operational" reasons. In effect, the reduced MNo has to be treated as an MNe and makes any claims about the aircraft's performance purely historical.
The linked thread mentions very high speeds for the B727, CV990 and Tu-154, but as these are all VC10-era jets they may also include misleading uncorrected IMns.