Back in the 80s when I lived in Bermuda and flew back and forth to UK a lot we did BDA-LHR in just over 5 hours on a Tristar , i think a 500. The captain remarked that it was his fastest ever Atlantic crossing and that the jetstream flowing from the south west almost the whole way from Bermuda to the UK was the reason behind it. Return trip three days later took a looooong time though.