Depends on person, I took AAMC 3 before taking any Bio or Organic in college, I got over 2/3 rds the Organic right. There is alot of info in the passage and you can pretty easily extrapolate gen chem knowledge to make educated guesses on organic.
Obviously you want to take organic before the test, but at least half of the questions are not out of reason for someone with a really strong handle on genchem.
You guys are both correct...some will struggle, others will be able to sift through the information.
The problem is that the stuff that you don't have to extrapolate from the passage in O-Chem is often ridiculously easily rote memorization you acquire over a year long traditional course. If you don't have your IR values memorized, or have your IUPAC naming down (both gimmees), and you can glean them from a prep book then do it.
But why burden your MCAT studying with learning an entire course? MCAT studying should favor technique over memorization, and you are cutting into your strategy and technique time by teaching yourself O-chem when you could be spending that time getting verbal down or focusing on whatever your weak area is.
Don't say I didn't warn you, however, but my real exam had 2 pretty nasty mechanisms that were both from second semester O-chem. One passage was on oximes and the other was a Grignard reaction (sometimes taught 1st semester). About 2-3 questions could be answered using passage information, but the other stuff was pulling straight from an
O-chem knowledge base. In fact, to answer the naming questions you had to know the mechanism of the reaction. You had to know where the nucleophile attacked. Basic O-chem, but knowledge-based nonetheless.
FWIW, I think if I was going to teach myself a subject it would be O-chem before physics. You will definitely see material out of the scope of high school physics on the MCAT. Waves, optics, and some people have even been lucky enough to get modern physics on their test.