Extract from the Chapter entitled Vickers Vanguard from Brian Trubshaw's excellent book, Test Pilot:
"Another interesting feature of the Vanguard was the relatively high speed envelope. Demonstration of this was made by flying down the design speed diving line (VD). At about 12,000ft the design limit was some 400kt.".....the aircraft itself handled beautifully...".
He also describes flying the Vanguard on a sales tour between Cairo and Beirut "...did the trip in one hour and five minutes flying at 1,000ft at over 300kt indicated...."
I appreciate there are some gaps in this data and Trubshaw was of course a test pilot flying a manufacturers prototype, but seems the Vanguard was a speedy machine despite being "....a great tub of an aircraft...." (Trubshaw)
Trubshaw records he was rather fond of the Vanguard but his test flying of the type was interrupted by the VC10 development.