According to my teacher 80%+ is an E4 for 3U, and 60%+ is rougly top band for 4U, this is however, just an estimate to aim for, like this year, the papers seemed harder, so they may adjust banding etc to suit i would think, otherwise no one is gonna end up with a top band.
And i dont necessarily think canditure gets smarter each year, but according to to people i have spoken to, and past papers i have looked at, the hsc maths exams have been getting easier each year, except for this year it would seem....