There is apparently an "improved" current sensor that powertune uses on the GHz Edition, but other than that and some possible binning, the cards are physically identical and should be able to use eachother's BIOSes without issue. Boost is apparently possible on the old cards as well, not that it would matter to most OCers.
Shouldn't need any specially leaked BIOS, just any BIOS from any 7970 GHz Edition that is from a card with the same PCB.
...rightful liberty is unobstructed action according to our will within limits drawn around us by the equal rights of others. I do not add 'within the limits of the law,' because law is often but the tyrant's will, and always so when it violates the right of an individual. -- Thomas Jefferson