Thanks, Ian - as I've been saying, the song (and musical) side of things may well be related to the storytelling, but no one seems to know how far the connections go as we simply don't have the evidence (as far as I've been able to ascertain) about how stories were performed/presented/told. As Aucassin et Nicolette is referred to as a cante-fable (and I haven't checked how far back that label was applied) it seems reasonable to assume that it was considered a different style from the romances etc.
I have been interviewing a number of storytellers as to length of performance and how far their performances are informed by historical evidence, but so far haven't found anyone who has based their work on anything medieval. I have, however, found lots of people who happily refer to troubadours and minstrels as if they were interchangeable terms, and people who assume that contemporary songwriters are the same as bards and troubadours, and people who assume that troubadours and minstrels carried news around the country and all sorts of happy misconceptions. Sometimes movies and tv programmes have a lot to be responsible for!
Also in terms of length of performance (for long stories) the stamina of the reader/teller has to be taken into account with the attention span of the audience ...and the opportunity in general life to sit still for a number of hours without having to worry about tasks and food, lighting and other practical considerations.