Upgrading from Drupal to Pressflow

I have drupal based website (Drupal version is 6.19), it is very heavy content website (about 400K articles in it).

By following Rule one of using Drupal, I didnt make any change on the core. but i have a lot of enabled modules and some of them were customized.

Now, I am suffering of the performace and I need to enhance it. I never used Pressflow before, but I have read some articles saying that pressflow is better than Drupal. is it safe to upgrade from Drupal to Pressflow? and if so, how to do it?

Thanks for your help

Solution

Pressflow adds the following features to Drupal.

Support for database replication
Support for Squid and Varnish reverse proxy caching
Optimization for MySQL
Optimization for PHP 5

Pressflow is a 100% api-compliant replacement for your standard Drupal Core. There are no database schema changes. So long as you are running a normal Drupal core and meet the other system requirements (PHP5.x, MySQL 5.x), Pressflow is a "drop in" replacement.