I'm gonna stick with the Z270P (thanks for your advice.) I got 7 cards recognised at startup yesterday. I had to grind the front edge off of the M.2 connectors to get them to contact properly. The PSU is 1200w, it may not be enough to mine with 8 cards but it will be enough to start a system with no load on the cards. I also have a link cable and spare 550w PSU I can add if I need to.