don't do it brah
Senior science is terrible, I have a mate who did the exact same thing, dropped chem for senior science
he regrets it (i can see it in his eyes)
As somebody who goes to a shit school, it varies lots, you can't say for sure.
For example, my school achieve 1-2 B6's in physics each year. Then last year, we got 6 B6's.
I don't think there is any advice anybody can give you.
You seem to be looking for a short cut. You should've realised long ago there wasn't one for trials preparation, you've just got to practice.