Convert MySQL Database to MongoDB

I have a Zend PHP Application (www.sikher.com/guru-granth-sahib/) currently using MySQL for all data storage. I want to move to MongoDB, as I have heard it is more efficient/faster and there are less data locking issues with it. The MySQL database is currently about 800MB big.

I would like to know from all bidders:
(1) How much faster is MongoDB than MySQL? Is it worth switching over?
(2) How much time could this take to implement? Will there be any down time?

I'm a very flexible and open minded project manager, and looking for a developer for further projects too.

Thanks for your bids!