I'm a Year 11 Suzanne Cory student and I'm pretty sure that what results gets you in depends on the school that you go to. Generally, people put Macrob and MHS as first preference, so generally people with 4 superiors and above go there. I put Suzanne Cory as first preference as I didn't want to travel and got 4 superiors. There are many in my cohort who have gotten in with no superiors, as well as with 4 superiors (me and a few friends). I'd say the average Suzie student gets 1 or 2 superiors and a couple of high averages or averages. If you get top tier marks (for my cohort it was 4 superiors and above) they'll gobble you up with no interview, as it's rare for those people to prioritise the school as 1st.
The school adopts a 5% quota where they take the top 5% achieving students in your school. If you go to an academically bright school (like Uni High's AP program that's where I went) then many people should be getting top marks (in my school the highest was 4 superiors and around 10-20 people got it and got into their first preference). If you go to a not-so-great school and you didn't get the top marks then it comes down to luck on whether SCHS chooses to pick from your school. If you got a few superiors and didn't get in, then Suzie might have adopted the 5% rule and only taken the top, or maybe it completely disregarded your school for some reason. If you don't score top-tier marks then sometimes it really can only come down to luck.
You've probably heard of students getting in with no superiors. Either that was complete luck, or they did amazing in their interview. You can definitely get in with less than 3-4 superiors, but it sometimes comes down to luck and if the school decides to adopt the 5% rule with your school.
All the best!!