This actually differs across subjects and GAs - for example, check out the grade distributions for
biology and
economics. For GA1, an A+ in bio was anything above 93%, but for economics it was anything above 89%. Then for GA2, an A+ in bio was above 90%, and also above 90% for economics. So, across four GAs, we have three different mark ranges for an A+.
This is also only the trend for last year - different years might have had different cut-offs.
If you're really interested in this kind of stuff, you'll have to look at the
grade distributions (preferably across several years) to come up with a nice mean across each subject.
EDIT: in fact, for something really outrageous, check out the distribution for
methods from last year. 2013 had the hardest exams for methods I'd ever seen, and this is reflected in the grade distribution - while exam 1 (GA2) has a respectable range of above 89% for an A+, exam 2 (GA3) only required for any student to get above ~77% for an A+ for that whole GA.