Buster,
70% prior to the brush should do nicely! Incase you or somebody else finds it useful, my general feedback technique for the exam is:
Just keep redoing the feedback again and again until you have every question sussed. If you do this you will learn a suprising amount too because of the cross polination between similar questions with different answers and looking up unexpected answers.
My technique was to use a light pencil that can easily be rubbed out so that you can't see at all. I do the feed back and mark it. I then rub out my answers and mark the questions that I got wrong or felt that I was unsure about. That paper would go to the bottom of the pile. I would then revisit that paper next day or maybe in two days (long enough to forget) and answer only the questions that I marked. I would expect to know all the questions by this point. It takes about a day or two to go through all the BGS feedback for a module so this works out pretty well.
The day before the exam I remove all my marks from all papers and do the whole lot again in one big go! By this point you should be getting 99.999% on all the feedback. The amount of spare capacity and time this gives in the exam cannot be overrated.