My brother got 76th percentile in 2012 graduating with an ATAR of 99.90 but he didn't receive an offer to Monash.
Meanwhile I got 68th percentile which I'm satisfied with considering I didn't do prep and it's enough to get into UTAS for Tassie leavers 
I had 75th last year and managed an interview at monash. That being said, with umats between low seventies and mid eighties, youd probably want a very high atar to compensate. Monash have changed the way they go about selections for interviews, so dont feel terribly disheartened with a umat within the range i just mentioned. I know that might be hard at this point (trust me, i get the feeling), but its important to try and move on as quick as possible as there is vce to still focus and do your best on; you dont want to let all the work youve done over this last year to go down the drain. And after all, as cliche as it sounds, there are still options out there like jcu, particularly for those who wouldnt mind going interstate to study.