Just took my step today, and it really isn't all that surprising. The format is the same as UW, complete with lab values + search options, calculator, color inverter, the whole shabang. As for the content, I'm surprised at how little memorizing random FA facts helped me. I mean, maybe I just didn't remember them enough to be able to apply them. But, overall I would describe the exam (at least for me) as more of a higher level, conceptual, apply-what-you-know-to-reason-a-sensible-answer type of exam. I actually found myself learning things from doing the questions. There were a couple of WTF questions that everyone hears about - don't sweat them. Chances are they're experimental. Just move onto the next question and forget about it. I had a LOT of behavioral. I think I had 4 or 5 questions just on coping mechanisms (eg splitting, suppression, etc). Which was very nice

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Disclaimer: I mark any question I'm not 100% certain on. Having said that, I marked about 10-15 questions per block. I normally finished with about 10 minutes remaining to go over my marked questions.
Here's my progression:
January baseline from school exam - 192
February NBME 13 - 222
March NBME 13 (again because my school is unreasonable) - 232
May NBME 15 - 256 (this exam hit all my strong areas)
May NBME 16 - 245
May NBME 17 - 245
June NBME 18 - 245 (hopefully this pattern continues

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Anyway, I'll repost when my scores are out. I hope this eases any anxiety of the unknown for any other neurotics like me (who am I kidding, most med students are).