php: best system/cms for building social community system?

our company needs to build up a professional social community site with extensive features like: profiles/groups/add friend, image + video upload, articles + tagging, activity stream, login/interfaces to social sites like facebook, twitter, foursquare, vimeo ..

what would be the most powerful system/extension? the most important factor would be: speed! as we also want to do most of the gui customizing by php on 开发者_JAVA百科our own, the cms/system shouldn't be too static.

thanks

I will suggest you to use Joomla + Jom Social