Sorry to say, but it depends on the uni, because a competitive ATAR changes based on the uni (e.g. for one uni, 99.70 might be competitive, and for another it might not). It will change based on your UCAT score depending on the uni (some don't use UCAT, and for some UCAT is a very minor component of determining if you will receive an interview/offer invite). Your question really can't be answered generally as you want it to. It's always good to aim for the best ATAR you can achieve to ensure you are as competitive of an applicant as possible. If you do very well on the UCAT, you will definitely be more likely to receive an interview/offer invite. This doesn't mean you will receive one or you won't, but you are more likely, provided you also get a good ATAR.
Hope this helped.