First FreeNAS Build & on Xen Server with HBA - is my performance testing expected?

[Waco]

Realtek NICs are pretty sensitive to driver config and, surprisingly, samba config. I'd rule out the samba config until you get your iperf tests up, though. There are a variety of offloads in the current Windows Realtek NIC driver that actually hurt performance pretty dramatically with small packets and streaming throughput. Interrupt moderation is worth disabling if you have some spare CPU cycles as well as any kind of offload that the driver lets you disable.

Between driver tuning and changing samba configs I was able to get a flatline 112 MB/s out of my junky Realtek NIC in my last desktop client, so it is possible.