Anything less then a 7870 seems a bit shy for gpu power.
don't forget that there is still an year before the release.
by then you can bye an equivalent graphic card for less then 200$, probably half of the console price.
cpu power was what keep the current generation afloat and allowed for games to evolve. On gpu side they could always lower the resolution and effects. At least an 8 core jaguar is to be expected, 50mm2 is not that much.
jaguar seems the better choice since it is made on 28nm same as te gpu, its low power, high efficiency, low die area and best of all made by amd, so they can keep the research all on amd field > cheaper
considering the 190mm2 die area of the wiiu, double that for sony and microsoft is not that far of reach.
so, speculating, around 7950 gpu power, 250-300mm2 plus 8core jaguar 50mm2
the power consumption shouldn´t surpass 150 watts considering that the 7970m on laptops can be kept under 100 watts.
150 watts sould be quite easy to cool noweday considering the advances in gpu coolers that can cool more then that in a dual slot space.
For 400$ in a year that should be the acceptable performance for this high end platforms.
just one more speculation of course