Yolk15 I assume you’re in year 11?
If you’re able to transfer into a 3&4 in year 11, then definitely go for an extra subject and do 6. However, if you plan to do 6 subjects in year 12, I would personally say it’s not worth it unless you absolutely need a high atar.
It’s perfectly possible to get 95+ with 5 subjects, but a 99.95 would be unlikely.
I say not to do it because as a year 12 right now, my free periods are absolute godsend and I can’t imagine not having that extra time to get work done. I think 6 subjects is a bit too much work and you might have to sacrifice some stuff in order to keep up.
It’s entirely up to you, obviously. If you feel like you can keep up with the workload without sacrificing too much, then go for it. I just personally wouldn’t be able to <3