Generally speaking, it can be difficult to justify taking more than 12 units in year 12. This is because of two main reasons:
- The workload resulting from taking more than 12 units can be overwhelming. As such, There may be a negative effect on your performance across your subjects due to insufficient study/preparation that is caused by the need to allocate study time towards an additional subject, which would reduce the study time available for your other subjects.
- Units that are taken beyond the minimum 10 required units are treated as backup units, which can count towards your ATAR in the event of unexpected unfavourable performance in one of your subjects, and can, depending on the number of backup units that you have, either halve or completely negate any negative effect that unfavourable performance in the subject would have on your ATAR. Whether more than 2 backup units are needed may be difficult to justify, as the goal should be to perform favourably across your subjects, rather than having too many backup units.
However, subject combinations that exceed 12 units are not uncommon, and many students who take more than 12 units still manage to achieve favourable results. Because of this, when deciding whether you should take English Extension 2, you should consider your performance across your subjects in year 11, especially the fact that you already experienced 12 units, and would therefore be able to predict whether you would be able to accommodate a 13th unit without impacting your performance in your other subjects.
With that being said, English Extension 2 is a demanding subject, especially for a 1-unit subject. You could take it and see how you go at the start of year 12. If you are able to effectively manage the workload, then great! If not, you can drop English Extension 2 and focus on your other subjects.
I hope this helps!
