I don't think they would start Shippuuden with KG... And as some said before I don't belive there is enough content for a movie. This makes an OVA a good choice... However I think they might (very probably not, but more likely than a movie) take it after the sand arc, after Gaara has been revieved, but before Naruto go after Sasuke, or maybe right before Naruto start with his wind training. This is only speculation of course.