My advice is contrary to many as I am not a big fan of acceleration. It might be worth one more search if you can find a really good school system where your son fits in.
We happen to be in one such public school system, and while DD is near the top of her class, there are a few that are even stronger. She has the confidence of doing well in school, and the benefit of fitting in with her age peers.
I would agree with this if it is a possibility. The main reason we agreed to accelerate our dd, who was already the youngest in her grade, was b/c we had no options where the type of situation you describe would have been the case (save for a major move). Dd is probably about two months older than your dd and attends one of the highest performing high schools in our state as a 10th grader. The fit is about what you describe for your dd in 8th: she's one of the strong students, in AP & pre-AP classes, but she's not so far beyond the other students that it is a cake walk across the board. I really don't think this is b/c my dd is more able, but just b/c we don't have enough of a population of somewhat similarly gifted & focused kids for her to find that fit among her age peers.
We've been fortunate, though, that she really seems to socially prefer her grade mates and even some older kids over her age peers. While she has a few friends who are close to her age, her closest friends are, for the most part, around 16-17.
