Have you used Enthuware and ExamLab mock exams? If you have not, I would strongly recommend you to use them, the formats are very similar to the read exam, and they cover a lot of ground to get you ready for the real exam.
I have used enthuware and K&B so far and I would say you should get the Java OCP Java SE 6 Programmer Practice Exams book from Berts and Sierra. When you can complete those tests successfully, I would say you are ready. The book tests are the hardest ones that I've come across. Here is the amazon book url