Cloud Dock U.2 Performance?

I'm considering either a Cloud Store Mini or a Cloud Dock 4 but I'm wondering what performance I could expect from U.2 SSDs used in the Cloud Dock? I understand that a SATA disk used in the Cloud Dock will be limited to SATA 2 speeds, but does the Cloud Dock impose any limit on a U.2 SSD beyond 10GbE?