So it looks like I didn't have enough power between the 2 power supply units to power 4 cards.

I'm running 3 cards just fine at ~700 Kh/s each. Now what to do with this other r9 280x..? Maybe I should upgrade one of the 750 watt PSUs.

Maybe I'm just bad at setting all this up and the 2 PSUs I have will do just fine for 4 cards.  Anyways, it's time for me to stop messing with it for the night.