Short article showing the impact of adding memory to the virtual machine running Exchange 2010 on top of vSphere. As you will see there is quite an impact adding memory can have on the amount of disk I/O generated. With the I/O numbers generated you certainly don’t need expensive EMC disk either!
The next link is to the first part of the series where they tested the impact of adding virtual cpu’s to the Exchange 2010 server(s).
What is interesting in both cases is the amount of cpu and disk for 8000 users in both of these test is EASILY within the capabilities of VMware vSphere….so virtualize already!