Vote.
EDIT
Grade boundaries for A/A* in the past years:
2010 71/81
2011JAN 65/73
2011JUNE 72/80
2012JAN 77/84
2012JUNE 76/82
2013JAN 70/77
2013JUNE 75/83
2014 74/82
2015 79/87
on average: 73 for an A and 81 for an A*.
I'd say based on the difficulty of the questions it will be around 77 for an A and 85 for an A*.