[Zope] Zope capacity planning

Hi folks. I was giving a class on Zope/Plone administration and one of the students asked about an "official" guide on Zope capacity planning. I searched zope.org, asked all mighty Google and wandered through both the darkest and lightest sites that say things about Zope with no success. Is there such a thing? Is there any reference these students can point to when they say they need half-a-ton of servers to serve their requests?