VM Guest Nic Performance

I'm running iperf to get some network performance reading and was wondering what other get in performance between 2 vm guests.

As test 1 I have 2 VM (Windows 2008 R2) on the same vswitch and the same subnet.  So all traffic should be internal to the host.  It doesn't touch the pNic or anything after that.

My iperf server cmd is: iperf -s

My iperf client cmd is: iperf -c IPADDR -P 1 -i 1 -p 5001 -w 64K -f m -t 10

I get consistantly about 1.47 Gbits/sec transfer rates.  I would expect it to be higher.

Should I be seeing higher rates internally?  I get even slower rate once I hit the Intel 10Gb nic and venture outside of the pNic.

The server is a DL380p Gen 8  with E5-2670 in them

Thanks!

Larry B.