Hi jedijeff,
When you say "it appears that the cpu features my VMs will lose in that new cluster" what features exactly are you talking about ?
I have personally configured EVC many times and in different environments but never faced any performance issue.
If you're really afraid that something happen to your productions VMs, I would suggest you to do the following.
Create a new VM or clone a VM in your old cluster (Nehalems CPUs) and migrate it to the new cluster. See if there is any issue during and after the migration. Monitor the VM for a few days and I'm pretty sure everything will be fine.
Hoping the above will help you out.
Good luck
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