Estimating your Exchange Server 2010 Client Access server capacity needs is a critical setup task. The Client Access server is the entry point for all users. In addition, the Client Access server hosts important services used by the other Exchange server roles. This white paper presents an estimate of the relative CPU weights of the different protocols on the Client Access server that can be used to produce a more detailed estimate of hardware needs when you design a new Exchange 2010 deployment or expand an existing one. As part of the testing performed while researching this white paper, the effect of MailTips and the cost of NTML versus Basic authentication were also compared.
White Paper: Understanding the Relative Costs of Client Access Server Workloads In Exchange Server 2010 http://technet.microsoft.com/en-us/library/ff803560(EXCHG.141).aspx