My advice would be to ignore the “focus on this not that” advice, and instead, to use your MCQ question bank (whichever one you have), and do random sets of questions that pull from all sets of materials, and do these till you're blue in the face, and then do some more. You'll be surprised how much *all* the topics are solidified by doing an obscene amount of MCQs, and by pulling them from all topics, it helps your brain think more in the way it needs to on the exam (since the exam doesn't go chapter-by-chapter).
More importantly, though, each exam is different. The official content outline can give you a guideline of what percentages all the exams average, so could tell you which of those 3 topics is officially tested least; however, your exam could be the one that tests it most heavily, or could be one that hardly has 3 questions on all 3 topics combined, cause it varies. So, someone else who had an exam that was 50% COSO (for example) might tell you to heavily study COSO, but theirs might have been the heaviest COSO one that's out there, and you might get one that has hardly any COSO on it.
Of course…Winston Churchill had the opposite philosophy – there's a story of him in military school following the study-one-thing-only method. (EDITED TO ADD: This biography of Churchill has the story in the last paragraph of the linked page: LINK TO GOOGLE BOOKS ). A test was being given that required the students to draw a detailed map of a specific country, and the country wouldn't be named till it was the time of the test. Most students, understandably, studied the whole globe, since all countries were fair game. Churchill, though, picked just 1 country to study, and knew everything there was to know about it…and luckily the country chosen for the test was the country he had studied. So of course, his map was great, and he got an amazing score. I'm not brave enough to do Churchill's style, but I guess that's why his name's in the history books and mine never will be. Also why most people who study one country failed the test, cause not all of us are Churchills. 😛
So, I'll stick to my “study some of everything, pound out MCQ's on random sets” advice, but if you think you're more Churchill than average-small-town-American, then studying specific topics only may be your cup o'tea – famous thinkers think like you…I'm just not famous enough to think that way. 🙂
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