4,1 / El Cap / Flashed 7950 / DP 1.2 boot problem

I recently bought a 4,1 single CPU and did many of the usual upgrades (X5670, 24GB 1333MHz RAM, SATA SSD, 802.11ac+BT4.0 card). My impetus for doing all of this is I had recently purchased a Seiki Pro 4K 40" monitor (note it is a proper SST 4K monitor, not one of their TVs) and my old 2010 Mac Mini couldn't do 4K at all. I almost bought a 2012 or 2014 mini but the fact that they can only do 4K @ 30Hz led me down the cMP rabbit hole.

Overall I'm very happy with my decision. But here's the...

4,1 / El Cap / Flashed 7950 / DP 1.2 boot problem