I was running them at something high like 750Mhz on the highest mV setting, it was only one unit doing it and I can't really believe that it would be viable to run them like that in the long term.

Currently, I've got the freq set to 588Mhz to get me somewhere near 800GH/s. I'll slowly up the mv settings until it stabilizes.

Just trying to find the optimum settings so I can set and forget.