Enrique Saggese, a senior consultant on the AD RMS team, recently wrote a new topic entitled AD RMS Architecture Design and Secure Collaboration Scenarios. It outlines infrastructure-design guidance for your AD RMS deployment.

The following abstract summarizes this documentation:
Here we describe the scaling scheme for an AD RMS infrastructure, we define sizing parameters for the server roles in an AD RMS infrastructure, and we describe logging characteristics of AD RMS that enable adequate performance monitoring. We also present real-world data regarding Microsoft’s own production implementation of AD RMS in order to enable you to perform preliminary sizing estimates for your own infrastructure.

I found this content to be helpful, especially the sections that discuss various AD RMS network deployments.