I got 85.00 & my school would be ranked in the bottom 50 schools and my ranks were all ~2-16/30-50. So not that flash. (Teachers saw the lack of effort i put in and were more tediosus in suppressing my marks and setting up where my ranking would be).
I did ~3hours study per exam, the night before.... For the whole year, because I didn't study for trials/mid years. I didn't have a book for Senior Science (recieved an exam mark of 90) and Religion2unit (Recieved an exam mark of 89) and general math i was away on holidays for "Annuities and Spherical Geometry" and cbf catching up and got an exam mark of 88.
But tbh, I did nuffy subjects. So thus, choose nuffy subjects if you're a lazy fuck like myself and more-so enjoy having a social life rather than committing to school studies and you should be able to do alright. Although; i don't know if i majorly fluked my exams, or what happened, but i have 3 friends who are all ranked significantly higher than me, and are supposedly way more intelligent, and we did practically the same subjects, and they all recieved high 70's and low 80's which copious amounts of study.
I'm going to add another factor; if you feel you can understand and regurgitate what you have learned without studying (i find it quite simple to remember things we learned at the start of the year) then that will also assist you if you don't enjoy studying.. Conversely if you forget things easily, studddddddy hard.
If i had gotten my exam marks, atar calculators tell me I would've recieved around 89ish, which is pretty good for absolute minimal effort.