And psu can now handle the load.
as a rule of thumb 60% on an atx works well 24/7/365. and 1300 x .60 = 680 watts.
Just realized that 1300 x.6 is 780 watts
Anyway, I kept changing the voltage down to 875mV for both core and memory and it is still stable.
How much is it safe to downvolt?, I don't dare to put any lower value.
I don't think its your PSU. If you want to eliminate your PSU as the culprit just run the miner with reduced intensity, basically run it at 50% and see if it runs then. It will use less power and you can see if its your issue or not.
Try what I suggested and get your motherboard manual and find out about the available lanes on your PCIe slots.
Do you think that the problem of freezing rig is not a pSU related problem? In my experience I've cleaned my mobo with cleaners then I also tried the randomly change my riser slot to my pcie but the problem remains.