Using Biostar Racing Z270 GT6: set maxTOLUD, did not set security settings (no option in Z270).
A few questions and problems::
1) Plugging in a second GPU (via risers, 1st GPU also via risers) causes the motherboard to black screen on boot. Here's a teamviewer screenshot of how it looks like (display stopped working when a 2nd GPU came in, had to remote in with teamviewer).
http://imgur.com/a/H5flW2) The closest PCIE to the CPU is a 1x, then a 16x. Which slot is considered my "primary GPU"? Is it the 16x?
I haven't tested this mobo, so I don't know good bios settings.
for 2x GPUs you will most likely not need to set maxTOLUD; a general side effect of this or the similar enable above 4g encoding is that the screen will be all black during boot.
the closest 16x is the primary