If anyone is searching for or trying to get 7 GPUs to work with the Gigabyte GA-Z270P-D3 motherboard that is linked in the original post, I finally got mine working yesterday.

Equipment:

MOBO: Gigabyte GA-Z270P-D3 https://www.newegg.com/Product/Product.aspx?Item=N82E16813128975
GPUs:
- 4 x EVGA 1060 6G SuperClocked https://www.newegg.com/Product/Product.aspx?Item=N82E16814487261&cm_re=evga_1060_6g_sc-_-14-487-261-_-Product
- 3 x EVGA 1060 3G SuperClocked https://www.newegg.com/Product/Product.aspx?Item=N82E16814487267&cm_re=evga_1060_3g_sc-_-14-487-267-_-Product
M2 -> PCI-E adapter: https://www.amazon.com/gp/product/B074Z5YKXJ/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 (Lucky I ordered the twin pack as one was DOA)
Boot Device: Samsung 32G Bar Plus USB 3.1 https://www.samsung.com/us/computing/memory-storage/usb-flash-drives/usb-3-1-flash-drive-bar-plus-32gb-champagne-silver-muf-32be3-am/
OS: nvOC v0019-2.0

Instructions:

• Install the m2 adapter as per motherboard manual (basically, use the little tool to unscrew the m2 screw, insert the adapter on an angle, use the tool to screw down) You do not need to attach the additional 4 pin power cable as you're not power the card directly from it. Make sure when you power up the machine that the little 3.3v LED lights up (mine was bright white)
• Plug in all of your video cards
• Download and install the Gigabyte Mining BIOS (currently BIOS MIN.8a) from https://www.gigabyte.com/MicroSite/462/mining.html Follow the BIOS update instructions but do not follow Gigabyte's BIOS tweak instructions. They don't work with nvOC!
• Your machine will now reboot directly to the BIOS menu as it can't read from the boot device without some BIOS tweaks
• Navigate to the BIOS sub menu and change Windows 8/10 features to "Windows 8/10"
• Change CSM Support to "Enabled"
• Navigate to MIT submenu and set Max Link Speed to "Gen2"
• Navigate to Peripherals submenu and setup Initial Video Output to "PCIe slot 1"
• Ensure Allow 4G Decoding is set to "Enabled" (it was enabled already in BIOS MIN.8a for me)
• Navigate to the Chipset submenu and change Internal Graphics to "Disabled"
• Change Audio Controller to "Disabled"
• Navigate to Power submenu and set Wake on Power to "Always ON"
• Navigate to Save & Exit and select to Save & Exit

Happy days, you can now use 7 GPUs with your Gigabyte z270!