I've sung for Brenda. Somewhere I've got a set of silver 1, 2, 3, & 4p 1990 coins, which was my 'fee' for singing at the Royal Maundy service at Newcastle Cathedral, where I was a chorister. I can't for the life of me remember what we sang though (though it could have been Zadok - I definitely remember doing it as a second treble.)
Though the chamber choir repertoire has its own attractions, there is absolutely nothing like being part of a big ensemble that is tight, in the groove, and just smashing it. I've done the Verdi Requiem with a 200-strong choir than knew it backwards, and it was brilliant.