M2 Slot or Pcie Card

I am picking up a ROG MAXIMUS IX FORMULA Z270 board tomorrow and wonder when I take out my Samsung 950 Pro M2 ssd from my Z97 system and put it in the ROG, is it best to put it in the m2 slot or have it on a pci card like I have now in my older pc.I have the m2 now on a Angelbird Wings PCIe card which keeps it nice and cool..Just wondering though if I will loose speed if the 950 pro m2 is on the card and not in the m2 slot..