You should do your best in all your subjects.
Try and have balance in them: you don't know how it will actually go.
I only did one subject that scaled up much (Methods). All the others either stayed around the same or scaled down.
If Latin/Spesh is not in your top four, they'll still get scaled as normal, just they'll be the 10%.
And thus:
Do not purposely do worse in any of your subjects.If a higher-scaling subject, after scaling, is lower than a low-scaling subject, you'll still do better having the low-scaling subject there.
Try to get as high a mark as you can, in all subjects. Though scaling is useful. And work intentionally - if you're finding that just a bit more work would significantly boost your scores in one subject, do it. (Case in point: I didn't learn probability until the weekend before the Methods exam. I suspect I got most of the marks for the questions I had time for, and thus significantly boosted my marks. However, this did mean I neglected other subjects more for a time during the exam period.)
Just do your best, I suppose.