Just watched a Lincoln Center performance by Emmanuel Ax, Itzhak Perlman, and Yo-Yo Ma. They paused between pieces to tell a little of the tradition behind the music and to show how close we really are to composers born 200 years ago. Ax once played a Brahms piece for Rubinstein, who corrected his tempo. He explained that his tempo had been corrected by Joachim, who conducted the world premier performance with the composer at the keyboard. That ought to be a pretty definitive opinion on the tempo.
Ma borrowed a famous Stradivarius cello to play the next piece. It had once belonged to the man to whom Mendelssohn had dedicated the piece. It is entirely likely that the composer had heard that instrument played. And between owners, the cello belonged to Jacquline du Pre. Seems incredible that the line to people we think are so remote from us is really so short.