The 7970 Matrix cards are pretty much unlocked, 1,4V on the core and that's more than enough for air/water. And with the hotwire you can up the voltage even more. No soldering or anything like that needed. The hotwire is not really needed unless you're running extreme cooling.
My 7970 DC2 Top is also unlocked, 1,4V on core(with the correct version of gpu tweak) but I cant adjust mem voltage for some reason. This card requires soldering for hotwire though. Might try that if I'm feeling lucky with my soldering skills, that would give me control over mem voltage.
And I hear the "new" 280X DCU cards have voltage control up to 1,3V. A step in the right direction.
I think the 290 cards will become beasts on water, seeing people running them at 1150Mhz with aftermarket air coolers. Might just get me a 290, I want one even more since finding out they can be unlocked to 290X.. hmm
🙂