Hardware sizing for Exchange Server 2010
The latest and greatest Mailbox Server Role Requirements Calculator v3.2 has some nice new sizing capabilities such as the ability to help you size the CAS and Hub Transport server in addition to Mailbox Server and Storage needs. This is nice since you no longer have to calculate the Hub and CAS server needs manually using the core ratio of 3 cores of CAS for every 4 cores of Mailbox or 5 Cores of Mailbox for every 1 core of Hub. It also has about 11 other changes to help smooth out the calculator use.
The Three UC Amigos : Hardware sizing for Exchange Server 2010