So. The motherboard-reported fluctuation in voltage is a bit disconcerting, but it is just as likely be caused by the inaccuracy in the on-board measuring equipment as by the real thing.
It is not at all clear what is causing your machine to shut down, thermal issues aside. You might just be pushing so far out of the thermal envelope for the CPU that either it or the motherboard's on-board circuitry simply says "Ummm... no!"
Liquid cooling should most certainly be considered. You could cool that rig with air, but the number of fans and the necessary airflow may just be enough to hover the case at about 10" off the surface...
(Yes, I am exaggerating)
The difficulty in using liquid cooling lies in getting past the hype - of which there is a fair bit in the industry, and, of course, the physical limits such as the size of the case, hose routing, placement of radiator, et cetera.