Lower performance issue on 4CPU AMD server

Hello,

I've got some issue with performance with Win7 x64 Pro as guest system.

I've installed proxmox on HP DL585 server (4x AMD Opteron processors -with NUMA, 64GB of ram, RAID1).

I've created guest VM with 2x 12cores processors (HOST type), 48GB of RAM (statically allocated), VHD as virtio raw device.

I've got serious performance loss, something about 20% in comparission to natively installed W2k8 R2 on the same server.

Maybe you have some tips for me, what I can make to increase performance?

Regards
Krzysiek