I always encourage simple and stupid testing before trying to bench throughput through VMs.

For example, take a good platform that you are comfortable with and put it on your storage network and connect it to your targets using the same topology you'd expect your Hypervisor to run on. Then test. I use a series of seq max throughput tests, max i/o tests and then more specific test suites made to simulate database servers or webservers or whatever.

This establishes your base. You cannot reasonably expect to get more performance out of your VMs than you can your Hypervisor.