Well think about it from a perspective. Senior science does not equal common sense. I don't do it but come on, science is a subject which requires you to learn new things not just rely on your "common sense" like in CAFS and to a large degree, PDHPE. Although lets look at the pros and cons shall we:
Pros:
- Back up subject incase you flunk.
- Pretty straight forward subject.
Cons:
- Low scaling.
- Need to catch up on 2 terms of work which can cause you to neglect your other subs.
- Pressure exerted upon you.
Now I ask you, is it really worth it to pick it up? I mean you could always focus on your other subjects and do well in them. You have 11 units so you are not completely at risk, although if you flunk one, 1/2 of it will count into your atar depending if it is a 2u subject. But looking at your subjects, I think they will suffice in being able to get you 90+ if you have enough dedication towards them. Is it really worth it to pick up senior science?