It will be very hard for you to get band 5 in all your subjects to be honest. Not even 10% of people get band 5 for english standard for starters. I would say you are looking at 68-70
lol you aren't guaranteed a high atar in any sense at all. James ruse may go close to 10 on average but im not sure. But it would definitely not be the 10 highest ranking students every year, it would very much change due to the externals.