When I was in high school and we did a group read of a book I had read years before, I was able to substitute a book that I hadn't read yet and do parallel assignments (that I often wrote myself) related to it. You might want to look into that as an option when you get into this situation, polarbear.
It sounds like the middle school teachers need to have a dialog with the high school teachers and divvy up the books in an appropriate way. It's not like there's a shortage of classics.
That reminds me, MegMeg, you guys might also enjoy some Anthony Trollope, if you're not intimidated by thick books. Start with The Warden and/or Barchester Towers and see if you get hooked.
