Your mark of 80/100 for School Certificate English places you in the top 39% of the state.
Based on enrolment statistics from the 2008 HSC and some very very very rough approximations, that might be about equivalent to being in the top 52% of those who will go on to do the HSC with you.
In 2008 about 52% of the HSC cohort took Advanced, 44% took Standard and 4% took ESL. Not all the best students do Advanced though, there is a reasonable amount of overlap.
This would (again, very very roughly) put you above about 75% of Standard students and above 25% of Advanced students. (Remember that they scale the same so both positions would give you the same scaled mark.)
Having said all of that, if you want a UAI of 85, you are going to have to do a lot better in English anyway or otherwise perform extremely well in your other courses.
If you are willing to put more effort into English, you might benefit from the higher level of conceptualisation required in the Advanced course.