Have you read 'Red Ball In The Sky', by the late Charles F Blair? It's one of my favourite aviation books, and contains a superb description of his record 7hr. 48min. New York-London flight on 31 January 1951 in his modified P51-B 'Excalibur III'. At one point, a mid-Atlantic weather ship told him his ground speed, as indicated by their radar, was 520 knots, which is how he knew he'd got into the jetstream as planned. If ever I visit the USA, I must make a point of going to see Excalibur III - if she's still visible at the Smithsonian...?