Personally I prefer whole texts, it's harder to discuss story structure and prediction with extracts. However I would agree about the drawbacks too, we never seem to finish a book! Last year we trialled using shorter books ( we have the Big Cat series) which managed to nearly solve both problems. The range of books isn't there obviously so we compromised by using a bit of both! The Big Cat books would take a couple of sessions to get through, I think I did 2 a term and any extra weeks we looked at poetry ( The Lady of Shallot was a HUGE hit!) The books are also levelled, which helps!