Do they have gifted classes at his current school? Even if they aren't quite as robust as the ones at this new school, it would be a compromise.

IMO, "education" is defined in many ways. I think people tend to focus too much on book learning - the best parts of my education came from real life (and I'm an Ivy League graduate, lol). If it were my child, I would probably wait until he was a little older. OakLeaf makes an excellent point that a motivated child will find places to learn. I grew up on Florida's education system! He will find learning in family, nature, and life in general. Let him be a kid for a little longer and make this choice when it's better for him. That's my $0.02, at least.