I did bio 3/4 in year 11, and my friend did busman 3/4 in year 11 (along with chinese 3/4)
Both bio and busman are quite content heavy, and I wouldn't recommend doing either in year 12, as they take up a lot of time. Also, I believe both subjects are fairly easy to pick up without 1/2. Bio was my 6th subject, and I didn't put as much time into it as I should have, and I put far more effort into subjects I was better at in year 12 - my 5th subject had a scaled score of over 44
If you're willing to put in the time and effort into both bio and busman, as well as not neglect your 1/2s, then go for it! I think it's a good idea getting some subjects out of the way, especially with those subjects as there is hardly any advantage, perhaps even a slight disadvantage (due to not as much time) doing them in year 12. Keep in mind it is a lot of work, as you'll have four 1/2 subjects you'll have to keep on top of (do
not neglect these) as well as two 3/4 subjects which will each require a lot of time and effort. But if you're willing to put the effort into memorising and learning both of those subjects and are willing to work hard, a couple good scores before year 12 can ease off the pressure.
Whatever you choose, good luck!