I recently set up 2 Seagate Barracuda drives (ST3500418AS, ST3500620AS) in RAID 0. The controller is a add on card (UGT-IS100R).
I guess I feel it is a little low as I have another computer running 2 other Barracuda drives in RAID 0 with transfer speeds around 210MB/s, given though they are a different model and running off of MOBO RAID.
The difference in speeds between the two machines may be the result of the add on controller card. Vantec controller cards use software RAID as opposed to a dedicated RAID controller like a 3Ware or Areca RAID card. The Vantec card using software RAID in addition to the overhead put onto the cpu and PCIe bus could result in lower speeds.