A few answers and observations.
The winter 1956 schedule shows the daily Stratocruiser " Monarch" service as departing New York at 1700 and arriving at Heathrow at 1000 the following morning. Although no intermediate stops are shown it is probable that a technical call was allowed for, probably at Gander.
Travel on all the piston types, not just the throaty Argonaut, was very noisy and both the noise and the motion of the aircrafy could often be felt for more than 24 hours after arrival.
The Argonaut outlasted the Constellation probably due to its reliability, which stemmed from a number of factors including the wartime familiarity of air and ground crews with the Merlin. It was also easier to load than the long legged Constellation and in Tourist configuration had a more attractive cabin, three rows in the Constellation being windowless or almost so.
BOACs favoured hotel for delayed passengers in the days when most passengers checked in at Airways Terminal ( still there opposite Victoria Coach Station) was the Eccleston, just across the railway bridge from Buckingham Palace Road on the the left/eastern side of Eccleston Square. The building remains , though now converted to other uses, but the original hotel entrance layout is clear to see.
Each departing flight had its own bus from Airways Terminal with the destination shown proudly on the front,- very status enhancing for the passengers in the Earls Court Road!