If its a temperature problem, theres a system level component that's having an issue I would think.
Run a motherboard monitor and CPU monitor.... but a voltage issue could still be the case. I hope you are figuring your power availability per rig @ 120-160% expected draw? If I ran a 4 card machine I would be for sure running a 1600w power supply.....
I wonder if you are drawing too much +12V off the same rail that supplies the processor and are causing this all to happen.
I have seen many strange configurations once opening up power supplies and seeing what is tapping which available rail. Many PC power supplies have 3-4 independent +12V power supply circuits at roughly 50A each... give or take.... As far as knowing how they are distributed...... you have to open the power supply often to know the real truth...
You dont happen to be CPU mining at the same time are you?
I did try taking 1 980ti off that rail and add it to the 2nd psu along with the 970.
It crashed ... but I should try the new 970 all by itself. That maybe a bad card.. not sure..I did a rma on it and it also crashed.
I think the main problem is the asrock btc 81 pro cant handle that many high end cards running windows 8.1.
And the 2nd most thing was temp spin down time changing algo's which is fixed. I think.