Even though the scores are suppose to be standardized, I have heard that some exams tend to correlate better with your actual step score than others.
Is it number 3 that many people to seem to get a much lower score on than the actual step? Maybe someone with more experience than myself could give their input.
What I have heard from many people recently though is that forms 5 and 6 seem to be really close to the real thing in terms of scores.
Sorry that I can't give any first hand experience.
I scored a 231 on NBME 3 four days before my exam, and my actual score was 15 points higher than that. I realize it's tempting to try and predict your score based on these exams, but there are definitely some complicating factors.
1. I tried WAY harder on the real thing. I mean...give-myself-a-raging-headache, tapping-my-foot-frantically-the-whole-time-and-refusing-to-unclench-my-trapezius type of effort on the real thing. The NBME's, while it may feel like you're putting forth your best effort, just may not actually bring it out of you.
2. NBME 3 WAS a bit heavy on molecular biology. But so might be your actual exam. Either way, the scores are standardized, so unless you've just totally neglected molecular bio to a greater degree than everybody else, 3 wouldn't necessarily underpredict your score.
3. I studied like a maniac for those last four days. I think I slept about 3 hours total, scared into a near-manic state and determined to bring my score up.
I firmly believe that two things matter most:
1. The depth of your knowledge, a result of how thoroughly you read things (even if you feel you currently know NOTHING, it will come back to you in those intense last days of studying if you once knew it well).
2. The last few days. This is the stuff you'll remember most. I think those people who "take the last day off" are missing out on the most important part.
I also took NBME 4 two weeks prior to the exam, which gave me a 224. This felt easier than 3 but the scoring accounted for that (e.g. was much less forgiving).
Good luck, everyone.