The system has 16gb of memory, 6 GigE links and dual quad core 2.4ghz intel processors.

I have 4 bonded links in 802.3ad on my DSSv6 system with raid 6 configured on the 8 drives via the 3ware console.

I have tested across these bonded links to my 2 xenserver hosts and from within a VM I'm getting 200mb/s (mbits not bytes) write and 650mbits/s read, so not even using a full 1Gb link. To ensure there is no problem with the bonds or the switch I have another interface on my Dssv6 linked directly to one of my xenserver hosts and I get the same speeds. I've even tried to use mpio across the bond and the single ethernet and the speed remains the same.

These speeds are from monitoring the ethernet links via SNMP from both the xenservers and the DSS every 30 seconds

Surely I should expect at least 1gb/s write / read minimum.
Disks are datacenter (I think they call them ES, but cant remember) 1TB 7200 sata drives capable of 3Gbps