Well, according to the attachment in the post I quoted, maintaining an HD average over your first year of your course gives you a rank of 99.5 ish. Average that with your UAI, and then think about what sort of UMAT you'd need and how well you'd need to go with your interview. It's always best just to try and do your best, but that's a realistic assumption of what GPA/WAM you'd need to aim for--note the difference between a GPA of 6 giving you a rank of about 96, and a GPA of 7 giving you a rank of about 99.5. I don't think a credit average would do you any good, and a distinction may not be safe depending on what your UAI was.