The SSD Review published a review on the 8 PCIe & SATA M.2 SSDs Test ASRock's Fatal1ty 990FX Killer AM3+ AMD MotherBoard

A quote from the article:

To be frank, we started testing with two thoughts in mind, the first naturally wanting to confirm that we could attain PCIe 2.0 X2 performance, and the second was to validate that the M.2 connector could automatically detect M.2 SSD type and switch off, whether it be PCIe X2 or SATA 3. From there, well we just kept testing M.2 SSD after M.2 SSD until we ran out, eight in total and one that didn't want to cooperate with the AMD chipset.

 8 PCIe & SATA M.2 SSDs Test ASRock's Fatal1ty 990FX Killer AM3+ AMD MotherBoard @ The SSD Review