Upgrading from Pressflow The ultimate goal here is to take a somewhat large (about 15,000 nodes) and complex (many contrib and custom modules) site from Pressflow 6 to Drupal 7, so I am assuming I should make the shift to Drupal 6, then upgrade to Drupal 7. Is that the safest path? Is there a better way? And if this is the best way, I was curious about the strategy or things to think about when making the move from Pressflow 6 to Drupal 6.

I have seen a lot of things about going from Drupal to Pressflow but not so many going in the opposite direction. I did find this question: is there a safe way to convert a pressflow website to drupal 6?

But like everything I found about moving from Drupal to Pressflow, people just say it is a drop-in solution, but what does that actually mean? I have done a diff between base Drupal 6 and Pressflow 6 and I can see the differences. But if I do a diff on base Drupal 6 and our Pressflow 6 site there are a lot more differences and it doesn't appear that just dropping in the Drupal 6 core and overwriting what is there will turn out well (though I will have to try this as an experiment to confirm).

In short, I am looking for a more in-depth answer to how to migrate from Pressflow 6 to Drupal 6, other than just saying it is a drop-in replacement. For example, what files/dirs definitely have to be replaced, which files/dirs should you definitely not replace, what if any changes are required to the DB (my impression is that there are none), etc?

Thanks!
The only point is that you should disable and un-install the Pressflow modules, the rest is the same that drupal 6.

The big problem will be with the custom modules. The best always is try to make the migration.

If you don't want to migrate you can use feeds to move from drupal 6 to drupal 7. But in this way you must build the site in drupal 7.

Oskar