I’m stressing the word _helper_ on this because there are no guarantees. Sizing is completely site dependent. What’s right in one site might be totally wrong in another similarly sized site. It all depends on activity, failures, configuration, etc.
“The OpsMgr 2007 R2 Sizing Helper is an interactive document designed to assist you with planning & sizing deployments of Operations Manager 2007 R2. It helps you plan the correct amount of infrastructure needed for a new OpsMgr R2 deployment, removing the uncertainties in making IT hardware purchases and optimizes cost. A typical recommendation will include minimum hardware specification for each server role, topology diagram and storage requirement”.
The best advice I can give is to build an OpsMgr 2007 R2 test lab and get it right. Then do a limited and planned pilot on production systems based on documents and guides you’ve developed on the test lab. Then try to use the heuristic data you’ve gathered to size your production systems in addition to using the above.