I noticed a couple performance optimizations in 5.0.18 that look relevant to us:

Bug 38476 – Perf improvement for massively shared public calendars
Bug 37683 – CalDAV: cache ctag requests to improve performance/scalability

We have massively shared calendars (3 public calendars mounted by 3000 users) on a single server. We have a growing number of iPhone and iCal users. iPhone 3.0 native CalDAV is more attractive than ActiveSync because it can handle shared calendars.

It doesn't look like we can benefit from either 38476 or 37683 because we're running a single node. We are not running zimbra-proxy or memcached.

Is there a supportable way for us to start doing so?

Does the locking problem on 38476 affect us as much as I think it does? Rendering calendars takes time... though I suppose the delay could be at the client JS end.