I'm using windows 10, as I have told before I have successfuly build several rigs before, like 30 of them with no problems whatsoever ( using the asrock h97 anniversary, until my last batch and the recent out of stock situation), it seems that there is some bios issue preventing the z170 chipset from successfuly handling more than 4 gpu , but i havent found a workaround yet ( to be honest iwasnt able to even find someone developing a solution for that)