So I did a few tests, and this card has seriously impressed me. Individually, the ports are 5Gb/s, bonded you can supposedly get 20GB/s. There also seems to be a way you can bond the four ports together if the cables all go to the same storage device (I don't know of any such devices at the moment though, and I imagine they're probably right up there in cost with a Thunderbolt storage device). This card is pretty sweet it has four ports on it so you can have four external drives, but beyond that you can also set them up as RAID0, RAID1, RAID5, or RAID10, and JBOD. The card cost me under $150CAD, including shipping from the US. The Mac Pro doesn't have Thunderbolt on it, and the external drives equipped with Thunderbolt are prohibitively expensive right now, so USB3 looked to be a better bet. Since most external drives you buy these days are USB3, and the Mac Pro only has (and perhaps only every will have, if the rumour mill is true) USB2 ports, the only option I had for expansion was a USB3 card. I recently purchased the HighPoint RocketU 1144AM PCI-E 2.0 x4 Quad-Port USB 3.0 Raid card for my Mac Pro.

Usb 3 card mac pro