In Boulder (where all your neighbors will also be former Bay Area residents):
Friends School
Bixby School
If you do want to look at public school, the Adams 12 district has a strong gifted program and some excellent schools. Boulder Valley district has pull-out programs for gifted kids that vary hugely from school to school. The bigger schools have more of a budget for gifted programs.
One issue I wish I had considered earlier in choosing what town to live in is diversity. We moved to Colorado from a very diverse state where we had friends and neighbors from a wonderful variety of cultures. Now I think my kids are minimally aware of the reality outside the generally affluent & homogenous Boulder Bubble.
