We have an aggressive target to meet - updates out in 5 minutes. Updates are small, but alarm bells are now ringing in my head about OpenLDAP's ability to deliver this.
This doesn't address the rest of your question, but if you need quick updates, you should be using delta-syncrepl rather than syncrepl for its smaller change footprint. It's also been substantially more reliable than syncrepl in my experience.
--Quanah -- Quanah Gibson-Mount Platform Architect Zimbra, Inc. -------------------- Zimbra :: the leader in open source messaging and collaboration