Which framework for a project?

I am contemplating between three frameworks: Django, CakePHP and Zend. The project will include social aspect (members), will have a cart/checkout, lots of different forms and very heavy database usage. I would like to write most of my sql by myself but have only basic knowledge of web development. Both PHP and Python will be new languages to learn, I have programming experience with mostly C from the past.

What would you recommend for someone who starts from scratch and needs to learn a language/framework from scratch? I know both PHP and Python are strong languages for the web and Python is very strong for scripting which I will need as well (back end). Which framework will meet the needs of a large website (not just a simple blog) that might require caching in the future (memcached etc) and heavy db usage (mysql) so performance is important. I am not sure what will be an overhead of a framework. I will also need a db search functionality (Solr?)

Thanks for your help and advice!