Most likely it's that cpu voltage you may need to bump but make sure to verify a safe voltage for your specific cpu.
Also, you may have hit the ceiling of the cpu. Try bumping the multiplier up to achieve a stable 4.5, then work your way up to 4.6 when your confident about it being stable.
Also 70+℃ temps, even for an Intel product, is starting to push it.
Are you able to get the 4.6 running long enough to monitor the temps before it crashes?
Try bringing the noctua cooler fan speeds to 90+% too.
MB: Crosshair V formula-Z
CPU: AMD FX8350 (8-core) @ 4.7Ghz
RAM: Corsair Dominator Platinum (8x2) 16gb
GPU: AMD Firepro W8100 (8GB workstation card)
cooling: custom water loop ,Ocool Nexxus U60 420 triple radiator,
Swiftech MCP655-B pump, Bitspower Compression fittings
HDD: OCZ OCZ "Vector" 256gb
PSU: NZX Hale90 v.2 1200W