I recommend polling a wider audience. IPSec use among active members here is relatively tiny, and our knowledge thin. *
Consider posting to the misc@ mailing list. See
http://www.openbsd.org/mail.html for guidance if you are unfamiliar with the Project mailing lists.
* I use IPSec, but I employ simple ipsec.conf(5) configurations, and neither gre(4) nor Cisco products are involved.