I have some new new servers that I have put in a new cluster in vCenter. They are Haswell(E7-8891). I have my other 3 clusters in vCenter in Nehalem EVC so I can move around live(nehalem of course my oldest box). I would like to be able to continue to vmotion to this cluster until I get rid of my nehalems, but this Haswell is so far ahead of Nahalem. But it appears that the cpu features my VMs will lose in that new cluster shouldnt really impact them? We are not doing vdi or anything else. Just straight VMs. Maybe I am missing something, but is there a compelling reason to keep this new cluster not having any EVC and give up being able to vmotion to it? Ie I will lose LOTS of vm performance somehow putting Haswell cpus in Nehalem mode?
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.