It's not too hard, though some shelves are harder than others. My trick was 2 questions sources per shelf (pretest and lange usually) and blew all of them out of the water. From what I remember, our rotation averages were consistently above 70 although I think neuro was a little lower. Shelves aren't that hard but they are different than step 1 and you'll need to adjust to a new way of thinking (ie. next step in management, best diagnostic test, best confirmatory test, etc.). Vignettes will be more about the initial presentation of disease rather than like step 1 where they give you a lot more workup info because they were testing the basic science of disease. Doing a s--tload of practice questions will help you adjust to this faster, and once you do then 70 is pretty doable. 56 is a couple SD below the mean and a rather laughable level for passing imo, even though my school does that too on many of them.
