Allegri's Miserere (with trebles dynamically improvising in place of the usual static run of "high Cs" - though we do get some of these as well, even two at once) at the
Ash Wednesday Evensong from New College, Oxford under Quinney. My word the men sing the chant parts superbly. And here is a clip of Palestrina's motet Peccantem me quotidie: