A new OpenVPN Release Candidate is out and we have not tested it on either client or server systems yet and therefore unable to recommend it yet. It is unlikely to improve performance but it might solve some compatibility issues with Vista so if you are having problems there, you might want to give it a try.
Most of our users are either using the stable 2.09 release or Release Candidate 4.
Release Candidate 7 can be downloaded here.
Feedback will be very much appreciated.
OpenVPN 2.1_rc7 — released on 2008.01.29 (Change Log)