The PCIe/NVMe based M.2 drives are much faster than the SATA based drives as they do not have a bandwidth limit on them. Form factor is different... etc.
http://rog.asus.com/308552014/label...a-and-sata-express-the-differences-explained/
http://rog.asus.com/308552014/label...a-and-sata-express-the-differences-explained/