slow performance on windows 2008 R2 Server guest

[konabi]

Hi
I have slow performance on a windows 2008 R2 guest.
I am using virtio for the network card.
I installed the driver from this instructions: http://pve.proxmox.com/wiki/Windows_2008_guest_best_practices

c:\tools\bin>win32-i386.exe -t 192.168.x.xxx

NETIO - Network Throughput Benchmark, Version 1.32
(C) 1997-2012 Kai Uwe Rommel

TCP connection established.
Packet size  1k bytes:  40.38 MByte/s Tx,  16.20 MByte/s Rx.
Packet size  2k bytes:  42.69 MByte/s Tx,  13.30 MByte/s Rx.
Packet size  4k bytes:  52.25 MByte/s Tx,  18.98 MByte/s Rx.
Packet size  8k bytes:  58.89 MByte/s Tx,  23.79 MByte/s Rx.
Packet size 16k bytes:  71.30 MByte/s Tx,  26.81 MByte/s Rx.
Packet size 32k bytes:  67.79 MByte/s Tx,  33.57 MByte/s Rx.
Done.

Performance between two proxmox hosts are good:

root@proxmox-03:~# /usr/local/bin/netio/linux-x86_64 -t 192.168.x.xxx

NETIO - Network Throughput Benchmark, Version 1.31
(C) 1997-2010 Kai Uwe Rommel

TCP connection established.
Packet size  1k bytes:  112.22 MByte/s Tx,  111.94 MByte/s Rx.
Packet size  2k bytes:  112.19 MByte/s Tx,  111.71 MByte/s Rx.
Packet size  4k bytes:  112.25 MByte/s Tx,  111.95 MByte/s Rx.
Packet size  8k bytes:  112.22 MByte/s Tx,  111.71 MByte/s Rx.
Packet size 16k bytes:  112.23 MByte/s Tx,  112.00 MByte/s Rx.
Packet size 32k bytes:  112.25 MByte/s Tx,  111.90 MByte/s Rx.
Done.

I am thanksfull for any help
Sven