I saw one wonderful article, regarding the CAS sizing, and since its common between us that Microsoft has never shared such tool or information for the sizing of Exchange Client Access Server, so after had look on this information, I felt to share it with you guys. Here you go…

Exchange 2010 – CAS Sizing:

As you can see above that the Exchange ActiveSync is one of the resource hungry process on the CAS, so if you are planning to provide Outlook along with ActiveSync access to your corporate users, then you have to consider the more CPU aid to your CAS.
I hope this would be helpful for lots of people, who are in the process to plan out their Exchange 2010 environment