The E4 cut off should change each year; I personally think that this years exam was harder than in the past (I got 82/120 in the 06 paper and about 74/120 in this one), so I'd expect the E4 cutoff will be, as said, 75 give or take 5 generally, and hopefully less this year :P.
I think it's based on scaled marks though; I think a B6 is a 90+ scaled mark.
It all depends on the scaling really.
EDIT: Sorry, my % was about 74, not my mark, which was about 90.
In this case I like the news that 75 raw would be an E4
