If you can be in the Philadelphia area, there are lots of private schools - they are not specifically for gifted kids, but there are plenty of gifted kids in many of the private schools. As far as public schools go, Lower Merion, Radnor and Tredyffrin-Easttown are just outside Philly and are good. They don't cater to gifted kids, but there are plenty of gifted kids in those districts.

Of course, the private schools are pricey, and homes in the good districts are not cheap.