That assumes you spend the time to figure out correct answers. If you are going to take it but just see a score of how you are doing and maybe get practice on timing, I say spend the time taking an equal number of questions in world/qbank because at least you can see what the right answer should have been. My personal view is that, because there are no official released answers with explanations, the NBME tests are useful toward the middle of your study efforts, to see how you are gauging, but can throw you for a loop if you tank one toward the end of the study efforts. And without good answers you cannot really learn from it. So I probably would leave it be and only look at things for which you have answers with explanations. For what it's worth, the qbank/world databases have incorporated pretty much all of the released test question topics pretty decently, so if you have gotten through those questions, you won't likely see something on the real test that was on an NBME test and not in one of those banks.
