The source have been found:
HOF GTX 1080 Air cooled: Have vbios that allow 1.3V which means it can overclock up to 2.2GHz
GTX 1080 running at 2,5GHz is from a HOF card cooled with LN2.
Hall of Fame GTX 1080 series uses the iconic white PCB and fan appearance, 12-layer PCB, 15-phase power supply circuit and dual 8-pin auxiliary power supply interface, the new three-fan TriMax radiator (10% performance increase), as well as FlexHold special graphics support rods, special breathing light, pre-core frequency to ultra 1771-1911MHz.
In aid of liquid nitrogen, Hong Kong veteran Mad Tse overclocking this card will eventually exceed a staggering 2502MHz! At the same time enhance the memory frequency from 10GHz to 11GHz.
After overclocking, the card in 3DMark Fire Strike Extreme Lane scored 12735 points, 9000 points than the standard frequencies around improved more than 40%!
Allegedly, GTX 1080 public version of the card lock BIOS and voltage GALAXY Hall of Fame edition opens this limitation, overclocking voltage is applied to the 1.3V.
More surprising is that, GTX 1080 not only extreme environment in liquid nitrogen overclocking ferocious, some play under the same conditions of air-cooled, can reach up to 2.2GHz.