ASUS P7P55D Premium P55 Preview @ PC Perspective

"So, while ASUS has essentially doubled the speed available to the Marvell 9123 chip, they have done so at the cost of additional logic and traces on the board and without actually meeting the 600 MB/s theoretical speed maximum. Still, 500 MB/s is still much better than 250 MB/s and I think that users will be able to see a noticeable difference - once we actually get SATA 6G devices out and available."