[Zope] upgrades and stability

We've been using Zope 2.51 on RH 7.3. It's been exceptionally stable and easily handles our workload. We are now about to refactor the system, add new features, add multiple hardware servers, some with ZEO front-ends, go to an multiple instance organization, to scale up for another order of magnitude or two of users. We are having to rethink system security (e.g., SSL), backup strategies, and add fail-soft support. If we are going to migrate to another Zope release, now would be a good time. What advice would you give. Zope 2.6.1 would be the obvious choice although if Zope 2.7.X will be released soon it might be another possibility. Any advice? hidden gotchas? release schedule intelligence? Thanks.