Recently the Exchange team changed the guidance for calculating the megacycles for different processor configuration. The change is to use “Hertz per core of baseline platform” instead of “Hertz per core of new platform”

Initially, we adjusted megacycles per core with respect to the total megacycles of the system and derived this formula:

((New platform per core value) * (Hertz per core of new platform)) / (Baseline per core value) = Adjusted Megacycles per Core

However, that is not the correct way to look at normalizing the server platforms against our baseline. What we are actually interested in is how this impacts the active mailbox user count.  Therefore the new formula is:

((New platform per core value) * (Hertz per core of baseline platform)) / (Baseline per core value) = Adjusted Megacycles per Core

For more details, refer to http://msexchangeteam.com/archive/2010/09/14/456262.aspx