Well I guess the course with highest requirement would be in ANU
Nope, most of its courses have a lower ATAR requirement than that of Melbourne or Monash. E.g. All double degrees involving Law "only" need 95, whereas it's at least 98 at Monash, and back when Melbourne offered undergrad Law it was well over 99. The various PhB programs require 99 admittedly (though you can get in with slightly lower) but then again so does the Dean's Scholar program at Monash.
Then again, ANU's entrance requirements are not set so much according to demand, they're usually fixed each year. And the demand obviously isn't as high, because it's in Canberra. You see a lot of high-achieving country kids at ANU, because in order to go to a decent uni they'll have to move regardless, and a lot of them seem to choose ANU.
Well what I'm trying to ask is like. Has anyone changed their preferences based on their under predicted ENTER? E.g. they chose courses that are 80ish ENTER and got a 95 ENTER and changed their preferences because they thought its a waste to do a lower requirement course?
Wait until results come out; I'm certain we'll see threads on here about that exact situation.