Thanks, Brian, for your usual clear exposition of some of the issues around singing 'big' ballads.
But from a personal perspective, I don't always equate length with 'big'; to me, big also means having huge emotional weight - 'Fine Flowers in the Valley' is a 7 verse telling of 'The Cruel Mother', and 'Son David' is 'Edward' in 8 verses. And although 'Bonnie George Campbell' is only 3 verses long (or 4 if you repeat verse 1, which I think is justifiable in this particular story), it can require a 'big' effort to bring home all of the background without over-dramatising.
Hope this doesn't confuse the issue!