Just found a very interesting link - a database of MT roles, sort of like Aria Database. Partly for my reference, partly for anyone else who's interested. It's not perfect, by any stretch of the imagination - I highly disagree with some of the voice parts they've assigned to roles - Sweet Charity done by a soprano? - and some of the vocal ranges and age ranges are way off. I do not want to hear a 17 year old singing Donna Anna. The vocal development simply won't be there. But, there are some interesting ideas, nonetheless.