after taking the beast myself and finding out about other ppl's experiences, the feeling you get after the test all depends on the set of questions you get - but that doesn't necessarily mean that your score will be substantially different from test to test (i.e. I thought NBME 5 was hard and got the same score I got on NBME 4, which I thought was easier). People with an "easier" (I know, no such real thing) set of questions need to be a bit more accurate, which is why you need a very high percentage on the free 150 for a very good score, even though this may not be the exact case on the real deal. The level of difficulty is an extremely subjective measure...some of it depends on your personality I think. If you are a person who studies like crazy for the exam, then takes it with the mindset that you answered it to the best of your ability and knew that the hard questions would just be hard, you would come out perhaps feeling neutral or that it was ok. But if you go into that same exam feeling that you should be able to answer almost each and every question, you may come out feeling like you were run over by a truck.
My exam was of the hard level of difficulty. I scored 94% on the 150 free questions when I took the practice test at the center 3 wks out of the exam, scored upper 80%'s in UW consistently (average 81%) and did very well on NBME's (I took all of them for exposure to types of questions) and felt that all of the above resources were much more straight forward when compared to the real beast. i know that this feeling is a product of the difficulty level of my individual test and my expectations of the exam so I won't generalize from a single test taker's experience. im hoping that the curve will factor in, but now after weeks of waiting for the score, im getting to stage of indifference, lol. good luck to everyone!