That's right, Radeon 7870 GPUs as TPU reports today:

ASUS is said to be prepping the ARES 2, a dual Radeon HD 7870 graphics card:
ASUS ARES 2 will back two 28 nm "Pitcairn" GPUs with all components unlocked; likely factory-overclocked speeds beyond those of the HD 7870 GHz Edition; and a total of 4 GB of GDDR5 memory (2 GB per GPU system).

The card will draw power from two 8-pin PCIe power connectors, and will have a TDP of around 300W. It will take advantage of AMD ZeroCore CrossFire, with which it powers down the second GPU when not gaming, or with light 3D loads that the first GPU can munch on. With the monitor idling for a set amount of time, both GPUs power down. It's likely that ASUS will use a triple-slot cooling solution, despite the fact that the HD 7870 is a generally cool GPU.