1) Ruby on Rails is a good choice. It gives a very quick start, a very rapid ability to create new features.
Tool on php:
2) the Symfony2 Framework is very powerful and has a large number of ready-made code (bundles) that you can use ready to implement your features.
3) the Yii Framework is also very powerful, but he's currently one problem - Yii1 already outdated and it's not right to start a new project (especially a large), and until Yii2 is in beta, and also not ready for such large-scale work.
4) Drupal is very powerful, taking on (+modules), perhaps half of your chips. Now run across the drupallers and tell you more precisely. But it is similar with Yii situation is actively preparing for the release of Drupal 8, but when it comes out - you never know, maybe a month, maybe a year. By the way, друпал8 will be done on the framework, Symfony2... you Can try and Друпал7 to start developing.
5) an Interesting option may be Phalcon framework is made up of little more than full in the form of an extension, not pure php. It is powerful enough to select it, and it will be very quick - you will need less servers to serve your audience.UPD.
Here's another ten reasons
to choose PHP + Symfony to load project.UPD2
Article Handling 1 billion requests a week with Symfony2
(eng.), but they don't do this on a single server, of course.