Do I have to point out this thread http://forum.hwbot.org/showthread.php?t=68909
I followed this but a little different and was able to unlock voltages on a 7870 hawk and Asus DC2
So no need for ABX
Edit: Just to add I had to use a modified bios on the DC2 to increase powertune limts from about 150w to 233w (Same as Hawk) or the card would crash with about 1.35-1.4v