99.95 is possible without that ext 2 maths. My subject were adv math, ext 1 math, eng adv, chemistry, physics and business studies. I was on track for a 99.95 based on the trials and other performance throughout the year but messed up a bit in the HSC probably due to pressure of the scenario but still got very high ATAR (99.70), so showing it is possible to get high 99s without ext 2 math.
However, one thing you need to understand is that to get such an ATAR you have to basically state rank or be within state ranking (1-2 marks) for every subject. This entails getting at least 95+ HSC mark in all subjects and probably 1-2 of them needs to be a very high band 6. English also out of these needs to a high band 6, as it can often limit that ability unless you end up state ranking in like multiple subjects. The difference between getting like a 99.5 and to 99.95 in my opinion is a lot about luck in terms of the performance on the exam day. If you make any silly mistakes then basically even if you had that ability to get that top ATAR, you won't so it requires a combination of top level ability, very minor to no silly mistakes and ensuring you perform well in all subjects that contribute to the 10 units. So if you are trying to set this as a goal, instead I would set some type of lower range like 99+ or whatever based on your ability so you don't get disheartened if something goes wrong. Because I know from experience when I misread a question in the HSC and lost like 4 marks cause of that it was a pretty shit feeling.
