Am I allowed non-piano performances? Because if so, there are two - both with an orchestra I played with at university. One, playing Mozart flute concerto no 2 - everybody ought to play a concerto at some point in their musical career, it's wonderful - and two, the first symphony I played, Beethoven 7. Particularly that second movement, so beautiful if you can get the dynamics to build just right. I think pianists sometimes miss out on the feeling you get when you play as part of a group and the sense of joint accomplishment when you all manage to pull a great performance off together. It's hard to describe, but the hairs on the back of my nexk go up every time I hear that symphony, suddenly in my head I'm back on that stage with the orchestra being part of something so wonderful.
This season I've been invited to go sing in a performance of Mozart's Requiem, I'm not sure if I can do it due to work commitments but, oh, I want to!