I have to develop a site which has to accomodate around 2000 users a day and speed is a criterion for it. Moreover, the site is a user oriented one where the user will be able to log in and check his profile, register for specific events he/she wants to participate in. The site is to be hosted on a VPS server.Although I have pretty good experience with python and PHP but I have no idea how to use either of the framework. We have plenty of time to experiment and learn one of the above frameworks.Could you please specify which one would be preferred for such a scenario considering speed, features, and security of the site. 
Thanks,
niting
Most of the frameworks out there nowadays are fast enough to serve whatever needs you will have. It really depends on in which environment you feel most comfortable. Though there are nuances here and there, MVC frameworks share a lot of the same principles, so whichever you choose to use is really a matter of which you most enjoy using.
So, if you like Python more, there's your answer. Use a Python framework, and Django is the best. If you like PHP more (which I personally don't), you've got some more decisions to make. But any of the PHP frameworks are fine. They really are. Just pick one that looks nice with comprehensive documentation and get to work.
PHP Frameworks (CodeIgniter, Yii, CakePHP) vs. Django