We tried montessori for DS when he was 4 and he ran through their material so quickly they didn't know what to do with him. Starting your son earlier has bought you some time at least.
We live in NM which is ranked 49th in education. In spite of this, we have been able to put together a plan that works for our son. Our primary mode of operation involves grade skipping as there are NO G/T programs here. He is accelerated 5-7 years dependent on subject at a very small prep type charter that covers 6th-12th grade. The school is locted on the campus of our university and offers dual enrollment as well.
My point to all of this is that it isn't necessarily about being in a good district. The most important thing is having a school that throws out all of their preconceived notions about grade levels and ages and just dives in. We have meetings whenever anyone wants one. Teachers, admin or myself can request a meeting and it generally happens within a week. None of us has a clue as to how to deal with high school credits and right now, it doesn't matter. Push comes to shove, he can always take the GED. They put him the classes that work regardless of grade level.
Try to stay flexible, plans for these amazing little people can change in an instant. Don't think more than a year aead, it'll just make you crazy and always listen to your "mommy gut" when trying to decide what comes next.
Keep us posted!
