I tried this a while back. My results can be seen at http://miffe.org/bench/

The largest problem is that the NVIDIA driver refuses to work when it detects that it's in a VM. The workaround is to hide the VM status for the guest os, by using -cpu host,kvm=off and disabling the tweaks that makes windows work better (hv_time,hv_relaxed,hv_vapic).