It depends. If you can do all the mock test on first attempt with 95%, then you are definitely ready to take the exam. However, if you take the same test, say, three times and you have 95% on the third attempt, then it means that you have just memorized the answers. The best way to pass the certificate is to study hard some good book (e.g. K&B), without taking the mock tests and when you feel comfortable, you may start with the mock tests. Some mocks are harder then others - for example, if you have a stable score in ExamLab around 60% on the first attempt for all the tests, then you are ready for the real exam (and it may even look quite simple, after passing ExamLab).
To summarize, you should really be comfortable with all the exam topics before taking the real exam.
Hope that helps.