I'm hoping that we can ... meet together with a psychologist our DS currently sees so he can get some outside perspectives on how giftedness can make minds work a little differently.
I think this is a terrific idea. Having a personalized professional interaction can go a long way.
BTW - how far over to the Right Side the the graph does your younger child end up? 2SD? 3SD? The graph measures 'unusualness' and humans being what they are, 'more unusual' means less likely to get their needs met without special efforts. If you go back to the doc, ask her or him to help you estimate 'how unusual' your child is compared to the local school system. It's more about fit than it is about an particular number.
Best Wishes,
Grinity
