Pinax vs. Plone -- Dev time, flexibility, security?

Question

Trying to evaluate Pinax vs. Plone as platforms for developing a social network with some RIA capabilities and a solid permissions setup allowing the user to make content visible on a per item/group basis.

Would I be better off hacking Plone (and having to learn Zope, etc) or adding on/modifying Pinax with existing/new Django? Trying to weigh dev time, flexibility and existing strengths such as security in Plone.

Thanks!