I can only give you some feedback on Nueva.

If you are not applying at one of their entry points - K, 5 or 6th G - it is not easy to get in regardless of IQ. For example, this year they expect 24-28 applicants for the 2 to 4 open spots in second grade. Bay Area has very high number of gifted kids and yet, there are very few schools that cater to their needs.

Helios is too far from us so I never looked into it.