One other thing: the population of the school that your son would attend is hugely important. We, for instance, live in a district with a huge number of new immigrant families and a fair number of kiddos who are performing below grade level. While my kids would stand out in most classrooms, they particularly stand out in this school district. That has been good in that they very obviously need accommodations and that has been easier to see. In other districts where the parents tend to be smarter than average, their kids likely are, too, and they might have more classmates closer to their level. Obviously, your son will not likely have classmates as advanced as he is. But, I would strongly suggest sitting in on K, 1st, and 2nd grade classes at his potential school just so you get a more realistic sense of the level of kids both academically and socially at his school. You say that his handwriting is at a more age-appropriate level, and that may very well be true, but you don't know the level of the other kids and that might suprise you.
Also, make sure you get a copy of the curriculum for each grade level. Maybe when you meet with the school you can compare what your son is doing with the curriculum in order to come up with a workable solution.
