I have wondered how the science curriculum should be changed for gifted math students, the vast majority of whom will not become mathematicians.
The Avid Academy in California recommends
http://www.avidacademy.com/courses that a physics course be taken in 8th grade after Algebra I is taken in 7th, followed by AP Physics B in 9th grade, AP Chemistry in 10th, and AP Physics C and AP Biology in 11th and 12th, in either order. Usually physics is taken only in 11th grade in the U.S., perhaps because students do not have the math background for it in earlier grades.
The EPGY Online High School lists Sample Courses of Study with a focus on humanities, math/science, or advanced math at
http://epgy.stanford.edu/ohs/samplestudycourses.html . Like Avid Academy, its math/science track also has students taking AP Physics B in 9th grade.
