Any chance you can share your config.plist, kexts, etc ?
I'm trying to install straight to Sierra (without first installing El Capitan) and I can almost get there. The video is always the issue.
Everything seems fine until I install the video and then it goes to crap. I'm running F7c and my config is almost identical to yours with (mobo, i5, and 970).
I'm connected via HDMI, and once I try to install the video drivers, when I reboot, the loading gets to two thirds and then my screen goes to black. System still seems responsive as I can turn caps lock on and off.
I'll try waiting for a minute or two and seeing if the graphics kick in. This is frustrating as I'm so close, everything else works and I can boot off my install USB without issue.
I'd like to try patching with someone else's working files and see if that helps. Everything else seems to work: USB, ethernet, etc.
Is the issue likely that I'm trying to go straight to Sierra ? Somehow I don't think so since I can get everything else working.