It will be tough to gauge it, by old med school exams. But honestly med school exams are not that tough, just think you go through 300 pages and they ask say 60-70 questions, so you need to have a pretty good idea of everything to do real well. But these questions are not very hard at all if someone gave same questions but say you had more time to study. But they will ask harder questions in some undergrad courses. The trick is the time limit and they often teach 20-30% of what will be on the exam the last week right before the test. So you don't have that much time to master it.
Some question examples are: Like, p53 does all of the following except, or what happens if you sever the median nerve before the carpal tunnel. I mean these are not tough questions, but there is so much material, that if you read it and memorized it there won't be too much thinking its more or less recall. The trick is to sort all the garbage from useful material and that is where I find that lectures are very useful, b/c they more or less focus on things sometimes they outright tell you. But if they didn't focus on something at all, generally speaking they will not ask it. Also any topic that is amenable to APPLIED questions, they love to ask that.
I strongly believe that if you can pay attention in lecture or can tape them via mp3 or whatever, and get the most out of em. It saves you the anguish of asking what to study, then you just memorize as much as you can of that and anything else you can manage. But really I find people who do real well follow lectures closely, another method is to look at old exams and see what kind of q they asked in the past. However problem with that is, that every year they tend to focus on different things so to have a pool of questions they can ask from. So they are a good general guide to see what kind of detail is asked, but then again in lectures they tell you that. Word of caution if you go to lectures and are falling asleep then they are useless, you actually need to get info from the lectures, not just be present at the lectures.
I probably gave you way more info than you asked for, but I guess this topic goes with the OP's post.