For our manual overclocking tests, we used AMD's Adrenalin software. Our best results are as below.
When we first tested the 7900 GRE, AMD had locked the memory slider at 2316MHz so overclocking was quite limited. However, subsequent driver revisions have allowed the memory to be increased to 3000MHz, and I found the Hellhound was stable up to 2630MHz. We also maximised the power and GPU clock speed sliders, while settling on a voltage of 965mV.
This saw the Hellhound run at just under 2.7GHz, closely matching the Sapphire Pure for clock speed.
While the extra memory headroom didn't result in much difference compared to the other AIB cards when overclocked, if we compare to a stock-clocked reference 7900 GRE, the overclocked Hellhound is able to run 8-15% faster depending on the game – so the gains looks quite reasonably in that regard!
Of course, power draw does increase when overclocking, and we saw the Hellhound pull just under 300W – which is about 50W more than the stock-clocked reference card.