hey yer i did it, it was very difficult. every1 in ma skool who did it thought so too... im not sure bout da grade boundaries but ma teacher said that approx 70 % u r guaranteed an A. Plus since every1 thought it was hard then the grade boundaries will probably go down...
Looking on da bright side of things, theres still paper 6 to go and it should be easier considerin u can use a calculator... :P