Have you thought about gradeskips?  Perhaps the "so called gifted program" with one year older kids would be a good fit?  What about summer programs and afterschool enrichement.  It breaks my hear to hear about your son not feeling in-sync. 
When it comes to counting your blessing here are a few I can think of -
1) they both score similarly and are at similar levels of giftedness - I can't imagine how hard parenting twins who are of moderatly different levels of giftedness is
2) you school ability groups - my whole district has done away with that through middle school!
3) they have each other as potential friends
So, there are lots of ways to "skin the cat" - what are your main concerns and what have you tried so far?
Love and More Love,
Trinity