I seem to recall a statement by Eric Brown in one of his books that when they were doing high speed research with Spitfires i.e. vertical dives, they would reach a point where throttling back the engine had no effect because all the speed was being provided by the aircraft mass - and they were hitting 500 mph with a lot more drag and a lot less mass than a Tallboy!
Also I think it was Sir Stanley Hooker who once did a back of a fag packet calculation that a Spitfire flat out in level flight was producing about 1000 lb of thrust. Sabres got close to the sound barrier in level flight with about 5000 lb thrust.
So a well streamlined bomb with 12000 lb (or 22 000 lb) of gravitational thrust? Through the sound barrier easy.
