Premed,
Hey, I like your idea of saving some AAMC tests for later in the game. I think the scoring methods of the commercial tests are a little off. These scores probably underestimate your true ability. However, I don't think it would be a bad idea for you to take AAMC I and II soon to gauge where you are right now. While I and II are easier than the MCAT you'll take (especially the Verbal section), the scoring should hold for the Bio and Phys sections. The Verbal section probably not so much. AAMC IV and V are definitely your best resources for seeing where you're at, but again, saving those for later is probably wise.