I would suggest you to not just look at the absolute scores but also at your progress. Are you able to increase your score after each test? If so, you are on the right track. If not, you are not realizing your full potential. At the end of every test look at your weak areas and study them. Only after that you should attempt the next test.
Looking at average score will not tell you much because if you scored 60% in your most recent test, IMHO, you are not ready. But if you scored 75% in the most recent test, you are definitely ready.
Make sure you take all the tests. Take the "Final Test" in the end.