[Dovecot] v1.1.20 vs v1.2 & v2.0

I am currently running v1.1.20 and was wondering if there is any compelling reason to upgrade to v1.2 or v2.0?

For example is there any security updates in v1.2 or v2.0 that aren't included in v1.1.20?

The other major thing I would be interested in knowing is there any speed enhancements in the newer versions? I am using basic PAM Auth and Maildir mailboxes on a Linux box. Let me know if you need any more information to answer my questions.

Thanks, Adam