According to Arno Widmann, Julia Fischer (a professor of violin at Frankfurt's Hochschule für Musik, Theater und Tanz) performed at a New Year's concert in Frankfurt in which she played Saint-Saëns Third Violin Concerto on the first half and the Grieg A-minor Piano Concerto on the second half! These are both rather difficult pieces of music, even for the professional and by all accounts, Prof. Fischer acquitted herself admirably. In fact, again according to Widmann, both performances were dazzling.
I can actually fumble my way through a Mozart or Haydn concerto and I've even played through the Beethoven First (appallingly, I assure you), but the Grieg is too much for my stupid fingers (although I could play parts of it with my younger, less arthritic hands) and yet here is a woman who, having mastered one instrument to the point of teaching others how to play it, takes on another and triumphs yet again. Oh to have even a portion of her "excess" talent!
HT: MPR's Classical Notes