You might be pleasantly surprised after gaining him entry to the GATE program. I know you wrote before that in your opinion none of the children there are like your son, but that doesn't necessarily mean the program couldn't accommodate him at all, does it? They might turn out to be pretty flexible, especially if you convincingly explain what your son needs and provide evidence of his achievement level. The more I go on with advocacy, the more I learn to be thankful for any opportunity, even when it's not perfect. The grade skip sounds like a useful possibility too.
I personally wouldn't be concerned about the relatively lower working memory. It's still above average. I keep reading that gifted children often have relatively lower working memory and processing speed. Unless there's some reason to suspect a disability, it's probably just a quirk of his profile.
