The pullout might have the sole benefit of identifying more possible peers for him. It really will not even come close to enough for him.
Some private gifted schools are a mess and some are pretty good in that teachers understand the needs and challenges of their student body. Some seem to want everybody to fit on a certain mold, while others will understand how asynchronous and uneven the children can be. The social benefits of being with children more similar to him might be worth exploring. In any case, I would ask the school how many HG++ students they have. Well established schools might have good financial aid packages (need based).
