We recently ran into a performance issue with a Dynamics customer that was running VMWare 6. The issue is caused by incorrect support in the VMWare network drivers for a new feature in Windows Server 2012 R2. You can read more about this issue here:
There is a workaround for customers who don’t have Update 2 installed which corrects the issue.
If you see erratic performance while pulling large amounts of data, such as reports or form loads, then you might have this issue.