I think a whole grade acceleration will put him with his age group. I think it would be difficult to ask a school to keep a child at a year behind his age-mates while asking for more advanced curriculum past the grade in which you've enrolled him. If you are moving to a new school, he'll be making new friends, so it would be the logical time to move him up a grade.
If I remember right you said you held him back a year so I have to agree with this statement. A move would be a great time to make a skip. Then the school might also be more willing to extend subject acceleration like you are discussing.
It might be harder for them to validate a fourth grader doing sixth grade work versus a fifth grader doing sixth grade work, since most just don't understand this level of giftedness anyway.
It kind of falls back to some of what has been discussed with redshirting (I am in no way implying this in your case), the difference between a four year old needing higher materials and a six year old who could easily be in first or second needing higher materials. Throw in your DS's LOG and I imagine the waters just get to murky for some school officials to wade through.
Best wishes with your decision. I know it's very difficult to find the right balance, a magic ball would be very helpful in these situations. We just do the best that we can.
