I want to bring up a possibility that is currently occurring with my DS8, with AS. Because he is used to not being challenged, when he is challenged in school his nervous reactions get worse currently. He suddenly has more expectations of how much he has to work in school (new gifted coordinator who rocks, new TSS who wants to help him get ahead), and it is really stressing him to the point where he is having outbursts we haven't seen in a year.
I bring this up not to say that you shouldn't accelerate, but to bring up the point that just because his behavior might not improve immediately and might get worse, it does not mean that you have made a bad decision. I firmly believe that when we come out the other end of this, he will be much better off.