Highest ATAR is not needed for Adelaide - do note that these days, about half the intake is international (so 35 of 69), then of the remaining 34, probably 20 are postgraduate (my year has a fully qualified pharmacist and me - an IT/MBA qualified project manager) as well as students that have done anywhere between 1-4 years of university study (we have a lawyer, biomed science, pharmacy, optom students & a med student). So as a school leaver, you are fighting for around 14 positions. Mind you I got in with a UMAT of 87.
Admission process is this:
1) Score as high as you can with UMAT
2) Apply to SACE
3) If your UMAT is high enough, you get an interview
4) They rank all applications by interview. Number of CSP positions are known.
5) If you get above 90 ATAR, and are on the list, you get in.
6) They keep offering until they fill up positions - some got given as late as week 4 of sem 1. Mind you, most of the late offers were to internationals as the domestic students weren't the ones dropping out.