I have always assumed that you'd need to get 45/50 at least to get a Band E4...
But anyway. i got an exam mark of 46, an assessment mark of 47, and HSC mark of 47 and a Band 4.
I think it'll slowly get harder each year. But generally, work hard, and if you're in it to compete, don't pit yourself against the rest of your school, but against the state... works both ways. If you go to an english freak school, you might not do very well and think you're terrible. You might also top a school where the english is not quite as good in comparison, and bomb out in the HSC as a result of differences in standards...