So we made the decision to whole grade accelerate my 12 yr. old from 5th to 7th and it was successful, but it was combined with a move so the issues were different. I face similar issues to yours as we contemplate what to do with dd5.
One thing I would encourage you to do is to google the Paradise Valley School District in AZ--they have a really great gifted program and links to research in support of cluster grouping that could be a useful tool for you and other affected parents to advocate with.
