Hello tow-eric,
Keep in mind that when you use 2 vCPUs that VM's processing time must be scheduled on two physical cores simultaneously. This means that when the 2 vCPU VM is processing, the other VMs on the system are left with only 2 cores to work with.
Like others have said, only do 2 vCPU VM's if the application can genuinely benefit from it. It is much harder on a Windows machine to go back to a single CPU HAL than it is to go forward to a multi-CPU HAL. I hope this helps.
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Regards,
Harley Stagner