Why Won't GT 740 work GA-Z170X-UD5 TH + i7 6700K

I have this morning done a fresh install of El Capitan 10.11.5 on my new build:

Gigabyte GA-Z170X-UD5 TH
i7 6700K CPU
Crucial Ballistic Sport LT 64 GB RAM

I'm trying to use my existing EVGA Nvidia GT 740 graphics card with this setup but can't get it to work properly.

If I use SMBIOS Mac Pro 3,1
After Clover screen and a few seconds of progress bar, I get a black screen; then I get an intermittent spinning gear and some other artifacts on the screen, but never get to the desktop.

If I...

Why Won't GT 740 work GA-Z170X-UD5 TH + i7 6700K