Yeah, the hard thing for some med students and residents to grasp is that just passing boards is OK. No one will ever know (including you), or care, whether you essentially aced it or tripped in when at the last second they dropped a bad question you missed. Having absolutely no clue what the answer is to a few dozen questions on these kinds of full day exams is pretty much expected. This is why so many people talk about "high yield" preparation. There is essentially no way to ace these kinds of exams -- those who write the questions can't answer all the questions the other submitters write, and frankly some are quite debatable (though in theory those questions are culled). Instead, you try to do well on the bread & butter and classic-if-rare stuff, and snag a few extras at the margins.
Unfortunately a lot of people feel like they're on the cusp between passing and failing, and those people feel like that one question they might get by studying all night the night before the exam is going to actually help them over the hump. In reality, chances are a good night's sleep will save you more questions than cramming, but some folks can't find enough peace to sleep before an exam -without- cramming. Everybody's different. If med school & USMLE didn't prepare you for your psychology of taking a major exam already...