When I read "The Making of Pride and Prejudice" the first time I noticed that AD thought he could do it in five episodes - the horror, I shudder at the thought. He is quoted:

"Originally I thought I could do it in five episodes but, because of the needs of television scheduling make four, six or seven episodes a much more convenient thing, this was not a popular idea at all!"
Think of all the scenes we would have been able to enjoy if he had gone for seven episodes. *dreaming*