IF you are DEFINETELY doing Specialist in Year 12, do Math Methods 3/4 in Year 11.
I'd say the reverse actually. Those two synergise well. I did practically no work in Methods in year 12 and just relied on studying Spesh. Back then the only difference between the two was probability (where I lost my mark in the exam), and as far as I'm aware, now it's that and matrices which aren't in Spesh. Maths is largely about being 'in the zone' for me with regards to careless mistakes etc, and I found that having two Maths subjects by the end of the year meant that I was quite ready for both with not much extra effort.
On the other hand, Biology is quite a tedious subject which I can't imagine managing well in year 12 given how much content there is to cover. It suits year 11 far better as you can actually take the time to read further, rather than simply sticking to the bare minimum of work (just homework pretty much) in year 12.