The voltage thing is not at all far-fetched, because there are many processors that on modest motherboards, as soon as you try to overclock them beyond a minimum, they just won't boot. If you could test on another motherboard that allowed you to modify the Vcore, you would know for sure.

By the way, don't rule out updating the BIOS to the latest version, maybe there is some function related to voltage in the latest revision available, if you don't have it already.

Best regards!