I have two very different kids, a traditional highly gifted daughter and a 2e son with stealth dyslexia. I'll give you my experience and perspective.
My 7th grade hgt daugther really learned very little in school until middle school. She had learned everything on her own well before entering school. I had very limited success with teachers really differentiating for her. Sometimes they had her do "special projects" and I tried to get in a district that had a pull out g/t program. The best was a one day a week full day pull out. The social part and that one day was enough to make her happy. Was she shortchanged? Absolultely. We decided against moving her up a grade because she was so small and I was afraid for middle school. Fast forward to today, and she is in an accelerated middle school program, now learning lots of new things, and has a 4.0. She is socially doing great, lots of friends, lots of confidence. I think keeping her in the same grade was the smart thing to do. I wish they would have done more for her to accelerate learning, but those were the limits of the school system.
Now, my 2E kid, which sounds like your son, it is a different story. He was in the highest reading group in 1st grade, and now fast forward to 5th grade and we are really struggling in reading/writing. He really internalizes alot, and he feels bad about himself, even though he is highly gifted in math/spacial things. If I had accelerated him to a different grade, it would have been disasterous for him. The writing issues are profound and damaging to an upper elementary/middle school child. The homework load is almost too much because it takes him so much time to do writing, and he is exhausted. I want him to feel the top of the class in math and science because that is what he feels most proud of, while we work on the others.
I don't know what is right for your child, but I would say the social/emotional and peers become so much more important to the child as they get older. Just consider that piece. Also, if the school is really good at teaching 2E kids, maybe acceleration is an option. If they are rigid, it is really hard on them later.
Hope that helps to give you an older child perspective.
