No personal experience, but I can tell you that in our school, strong students are generally given the advice to go ahead and take the SAT-2 after the honors course. They do state that the class is felt to be adequate preparation, though also suggest using a review book. The exception is kids who know they will take the AP course- some kids then wait and take the SAT-2 after that, assuming it will result in a higher score. DD has a friend that scored an 800 on the bio one after the standard honors bio (she's a pretty strong student, don't know how much extra prep she did).
I guess it depends on whether your DS's course covered the necessary material, or if he feels he can fill in whatever holes there might be.
