Usually big high schools function as "schools within schools" in that your son will probably be in most classes with the same students, regardless of how big the school is because they'll be advanced/honors classes. There may be 6 sections of honors English 9, but it will shrink to one or two AP Eng 12. Same thing with the other subjects.

You are SO lucky to have a high school with "a tremendous academic program, a world class music program and a swim team"--Wow!