Performance depends on the workload in the guests, and as mumps mentioned the load on the host system. If you are using the VMs to run your asic work, then you should get native performance as long as you are not maxing out your host system. I used to run my farm on all linux vms for doing the cpu work, and just matched up 1:1 vcpu to physical you should get 95-98% of native on a good bare metal hypervisor.