FYI....for testing purposes only....
I bought (2) MNPA19-XTR 10GB MELLANOX CONNECTX-2 PCIe X8 10Gbe SFP+ NETWORK CARD W/CABLE from eBay.....pretty cheap ($48.00)including (2) SFP+ cables and it worked out of the box. Im using an older motherboard (MSI G41TM-E43) with only 2GB of RAM on a LGA775 Core 2Duo and Im getting 398.7 Write and 452.4 read when transferring files from my Mac Pro 3,1....the Mellanox doesn't work with my Mac Pro so I had to get a SolarFlare SFN5122F Dual Port 10Gbe PCIe Adapter SF329-9021-R6 ($44.00). Setup was straight forward and speeds are very close to my OWC Thunderbay IV in RAID 0
My current setup only have 4 SATAII ports with transfer rate up to 3Gb/s, ( 4 x 3TB Drives) so maybe once I move to a faster motherboard, speeds will increase.
Can anyone comment or share what could contribute for speed bottleneck as the numbers of drives start to increase? 8 drives, 12 drives etc...my goal is to build a 12 drive system (36TB)