[Dovecot] dbox verses maildir - advantages/disadvantages

I am migrating our mail server from Courier-IMAP to Dovecot. We
currently use maildir storage format.

What are the advantages and disadvantages of Dovecot's dbox format
over maildir?

Does anyone have any performance benchmarks for both? What do people
use to test performance?

We are running on a Mac OS X box (10.5.7) using Postfix 2.6.

Thanks,

James.