Agreed. No problem with splitting a script, as long as it's long enough to warrant it. Some books, though, would have no choice.
The sword of truth series has 11 novels in it, almost all of them are, at least, the length of the longest Harry Potter novel or longer. (The longest being only a few pages short of a thousand) They're so long, the final novel, Chainfire, was actually split into a trilogy.
At best, you could probably condense it down to eight or nine movie, but you'd have to leave a lot out.