[Dovecot] Directory Layout Performance

From a performance perspective: Which Directory layout is better:

1. All mailboxes are stored in a single directory and prefixed with a dot or
2. Maildirs using physical directories, such as: Maildir/folder/subfolder/

It looks like the second option -- File Sytem Layout (LAYOUT=fs) -- could spread the load in a better way ...... I do not expect a user reaching maximum number of subfolders in linux , but what about those heavy users with a lot of sub-folders: Is there a significant performance gain by choosing a specific
Directory Layout ...

Any Comments?

Regards,

Mario Antonio