I definitely don't think the Kaplan tests are accurate predictors of success on the Gmat exam. While for most people, it seemed that the scores were way too low for how they performed on the Gmat, for me, the scores were actually inflated.
Overall, I didn't feel like the Kaplan exams were the best preparation strategy (and I did ALL the Kaplan quizzes and CAT tests).
During your last week, I would say to give the GMATprep and the OG the most attention. For the OG, concentrate on the last 100 problems of your problem areas - those are the hardest. Also make sure that once you take the GMATprep test, go over ALL the questions and make sure you understand them thoroughly.
Good luck on your last week of prep!