Very good points above. It is important to be efficient in your studying. A lot of students say they "studied" for 8 hours. But there may have been a significant amount of facebook, email, youtube, myspace time in there. I'm guilty of that quite often.
As mentioned above, the AAMC practice tests are a very strong indicator of how you will do on the real deal. If you are getting scores you want and are comfortable, you should take the test.