Essentially, if you strongly believe that you will not be able to perform to the best of your abilities at your current school and that, by moving to the school that you are thinking of, you will be able to achieve your academic goals, then this could constitute a basis/added certainty in terms of this being a good decision. Your experience throughout year 11 at your current school (including performance/results) may enable you to make an informed decision in that regard.

It is important to note that changing subjects in year 12 may not be possible, even if the school that you are thinking of moving to offers the subjects that you wish to take. This is because students must satisfactorily complete the Preliminary course (i.e. the year 11 course) before they are eligible to commence the corresponding HSC course (i.e. the year 12 course). However, a transition from English Advanced to English Standard and/or Mathematics Advanced to Mathematics Standard is possible for instance.

Mathematics Advanced is more difficult than Mathematics Standard and is also somewhat superior with respect to scaling. One of the main differences between Mathematics Standard and Mathematics Advanced in terms of content is that Mathematics Standard lacks the in-depth knowledge of higher mathematics that the study of calculus would provide, which is instead included in Mathematics Advanced (and higher). Overall, assuming that a change from Mathematics Standard to Mathematics Advanced is possible, your performance potential in Mathematics Advanced is an important consideration, i.e. are you confident in your ability to perform at a high standard in Mathematics Advanced similar to Mathematics Standard, which would be consistent with your goals? This is because some students may be able to demonstrate favourable performance in lower-level subjects as opposed to higher-level subjects, provided their rank relative to their cohort is high enough and that they are able to perform well in the HSC exam of the lower-level subject.

I hope this helps!