The real thing is anywhere from slightly harder to significantly harder than the AAMCs. That said, you should do all the AAMC tests (they're decent practice), but wait until you've got all the content down.
Most people score around their average to slightly below average. There is a thread w/ a poll showing this. The peak is at the average being the actual MCAT score but there is a slight skew toward below average. That plus apumic's MCAT estimator seem like they would give a good estimate esp. if they agree.
I though they were similar in difficulty, actually. I only took 3 AAMC tests: 3, 9 and 11, though my real MCAT score was my exact AAMC average. If anything, I thought that AAMC 11 was a bit more difficult than my real exam; I scored lower on that practice than on the other two practices and the real deal, on which I scored 5 points higher than AAMC 11.
I thought the real deal was about the same difficulty as the AAMC tests. That may have been my particular test date, but there's no way the practice tests are harder than the real thing.
You will probably score in the neighborhood of your AAMC averages. I scored exactly what my average was in each section.
Each MCAT will vary in difficulty, but I believe the general consensus is that the real MCATs are harder the AAMCs and easier than Kaplan/TPR/etc. My Kaplan instructor actually indicated as much. But the curve for the harder exams may be more lenient so that you'll end up with similar scores. Therefore, the real MCATs may be harder, but you are supposed to get similar scores to your AAMC practice exams due to the curve.
My MCATs were much, much harder than any of the AAMC practice exams - especially PS. I didn't find AAMC 11 to be much different from the rest of the AAMCs. I haven't received my score yet, but I'm hoping the curve will level it out.
There's no way to tell. Don't fall into the trap of thinking SDNer majority opinion is necessarily fact. My PS(6/16) was most definitely easier, both in length of passage and type of question, which may mean the scale will be ridiculously difficult, something I never prepared for. Also my VR and BS were very similar to the various aamc practice tests in length and difficulty. The notion that your real mcat will definitively be much more difficult than practices is untrue. To prepare, do some more difficult concept heavy passages and some calculation heavy passages.
There's no way to tell. Don't fall into the trap of thinking SDNer majority opinion is necessarily fact. My PS(6/16) was most definitely easier, both in length of passage and type of question, which may mean the scale will be ridiculously difficult, something I never prepared for. Also my VR and BS were very similar to the various aamc practice tests in length and difficulty. The notion that your real mcat will definitively be much more difficult than practices is untrue. To prepare, do some more difficult concept heavy passages and some calculation heavy passages.