The following update on Process Planning was announced on 14th of September by the Microsoft Exchange Product team
Guidance Change: Calculating the Megacycles for Different Processor Configurations Formula
New Formula –
((New platform per core value) * (Hertz per core of baseline platform)) / (Baseline per core value) = Adjusted Megacycles per Core
Read the link above to get more of an understanding
NOTE:This guidance change is effectively immediately and is documented within the TechNet article, Mailbox Server Processor Capacity Planning. The documentation within the Exchange 2010 Mailbox Role Requirements Calculator will also be updated to reflect this.
IMPACT to Existing Designs:
For those of you that have already sized your systems using the old, invalid formula, don’t panic, your systems simply will have some extra megacycle capacity. The extra amount will depend on the difference between the MHz value of your processor and the baseline value of 3333 MHz.