The SSD Review published a review on the 2013 MacBook Air Disassembled and Benched Samsung 256GB PCIe SSD Performs at 700MB/s A quote from the article:

In just over a week since its release, the MacBook Air has redefined storage speed and become the first to introduce the world to the reality of the new PCIe form factor. It appears that when it comes to money, both Apple and Samsung can shed their differences with the new MacBook Air pulling off SSD performance of 700MB/s in an ultra, even before Samsung themselves, and while utilizing Samsung's own SSD.

 2013 MacBook Air Disassembled and Benched Samsung 256GB PCIe SSD Performs at 700MB/s @ The SSD Review