accelerating adv AND ext1 will be intense, definitely think abt whether you're more likely to perform accelerated vs unaccelerated. the benefit is that you'll have those subjects over and done with +familiar with the HSC experience. another benefit is that you have a "2nd chance", if u do shit in the accelerated HSC you could resit the next year HOWEVER this isn't a true benefit imo bcz ideally you'd wanna perform well the first time, or just don't accelerate at all yfm.
downside is that ur workload will be significantly higher, like more homework, more assessments some of them may clash as well e.g. prelims and trials. it's just a ton of work to accelerate multiple subjects esp smth like ext1 but still doable
I accelerated ext1 and I wanted to drop it many times bcz it felt impossible, but I pulled through
if u enjoy math and work well under pressure then go for it