We've had some threads on that leveling out thing... I don't know that there's a great deal of evidence on it. And there's a school of thought that some of that leveling out is due to forcing the advanced kids to sit through material they already know versus moving on to new content. Same stuff for everyone... voila! They all level out... or check out.
You are right, it is harder to move with kids. Especially kids like ours! Have you considered cities of around 600-800,000 people? Big enough to have some resources but not so big that everything is expensive and hard to navigate. We have been lucky (sort of) in that we're in an area of about 400k population that is within an hour or so of a university that hosts gifted weekend and summer events. Maybe flip the lens and look for strong pockets of gifted activities then draw a map from there.
