Exchange RPC over HTTP

So I’ve been working with Exchange for years now. I’ve always supported under 50 users. I’ve recently just started at an organization that has 300 users. They have one, reasonably robust exchange server. Now I understand that Exchange won’t choke on 300 users, but I need to back it up with some common hard facts. I’m getting ready to deploy RPC over HTTP, and I was wondering if you guys know of any case studies, or logical way to guage your Exchange capacity versus your users’ needs. Obvliously, bandwidth is a big deal as well, but when we are simply talking about one server with concerns of CPU, memory, I/O, what do I do tell my superiors?