Server is powered by dual:

Getting error "StalledDueToWriteCpu" on users mailboxes even when migrating only one at a time in console.  Migrating from 2007 to 2013.  Exchange server is VM under Hyper-V on Windows Server 2012 allocated 4 cores for Exchange VM.  We can allocate more if necessary, other ideas? 

I would suggest you to put your environment info in Server Role Requirements Calculator and see how many cores are required for the Exchange in VM environment...

Exchange 2013 Server Role Requirements Calculator v7.6 - https://gallery.technet.microsoft.com/Exchange-2013-Server-Role-f8a61780

Hi,

Looks like it was resource on the VMs causing the timeouts.

Try to increase the virtual processors to the vm then reboot.

Best Regards.

We will try that, thank you.  Do you have any experience with the processor listed above (in my original post)?  My co-worker seems to believe that the CPUs in the server simply aren't fast enough to handle what we're trying to do.  

We will try that, thank you.  Do you have any experience with the processor listed above (in my original post)?  My co-worker seems to believe that the CPUs in the server simply aren't fast enough to handle what we're trying to do.  

As Amit noted above, you need to run those the Mailbox Calculator and account for the SpecInt Rate of the CPU. Its can be a little harder when virtualizing to correctly size for the CPU, but that's the only real tool available.

Note that you should also ensure the power options are set to High Performance on the host and you aren't limiting or over-committing CPU or MEM resources.