I found Ruf to be pretty accurate for our son and some of her suggestions to be very helpful in understanding him, but he was older (6) when I read her book, thus more history to review/compare. Your child's personality has a lot to do with his fit for particular schools, so think carefully about that as well as how smart/advanced he is vs. others his age. I happen to have a child who is very polite from a manners standpoint but who doesn't sit calmly in his seat and listen to lectures on material he's already covered.
If it were me, doing it all over again, I would spend a lot of time visiting schools (meaning same school, seeing the classroom and most importantly, listening closely to what the adminstrators say when you describe your son... are they condescending? do they brush what you describe off? do they talk about how that might work or not with their program, etc.) Run like he** from rigidity. Look for places where he can advance as needed. Montessori, and by that I mean good, accredited Montessori schools with flexible teachers who get excited when kids learn and grow as fast as they can, can be a good fit, in our experience. It typically has mixed age groupings, which worked very well for both of our boys.
