Ok what are you virtualizing and how are you going about the virtualization process will effect benchmarks. If your using W2K8 as a host OS then all your VM's will incur a performance penalty from the overhead produced by the host. If you use something like VM Ware ESX server then there is little if any overhead penalty. Something like Solaris 10 zones will incur zero host overhead penalty due to how they go about virtualization.
SQL can be virtualized fine using VM Ware ESX, even clustered. We've had big problems using W2K8 Hyper-V and SQL, we wouldn't recommend Hyper-V to anyone looking for an enterprise class service.