As I understand it, you can't adjust the voltage in Linux unless you modify the bios of the card.
This is purely a Windows parameter [citation needed]
I had exactly the same behavior, firstly SICK then DEAD on my 280X (Windows), when voltage was not in pair with engine clock (voltage too low or engine too high).
Did you tried to run it without engine and memclock parameters, just on reference (bios) clocks?