Hi! I'm interested to see what you decide. My DS8 is in 4th and just started the new school year. He is already expressing frustrations with the math curriculum. He could use some acceleration but I'm not sure if I'm ready to take on the system to make it happen. We are military and moving next summer so in our case, I would rather put my energy into finding a good fit for the future than try and push our luck with a system that has already bent a little for him.
He skipped in 1st grade into 2nd (after about the first third of the school year). We've had a wonderful experience with grade skipping (other than it wasn't quite enough to fit his academic needs). He says he would happily skip again for academic reasons but now that he is older, he doesn't want to be "too" different.
I think all of your concerns are valid but really down to the individual child and family. A big component I identify with is having an older "not as highly gifted" son. DS8 has a 5th grade brother who is 10. How giftedness impacts the family as a whole is something to keep into account. It seems like most highly (also universally) gifted kids can bridge any academic gaps efficiently - they just need to be given access and opportunity to more challenging work. It's the psychological aspects of acceleration that are more difficult to navigate. They are much more complex.
Without real experience parenting gifted children through middle and high school, I must say that from our current perspective, it appears that academic opportunities open up as you escape the limits of elementary curriculum. I hope that is the case. : )
