It's 8x the current generation transistor budget:
500m x 8 = 4b
I'm not expecting anything less than this for next gen.
I would estimate that the GTX580 is at least 8x the current gen console GPUs (probably >10x when compared to RSX). Yet it does this with *only* 3B transistors.
I'm just saying, 8x performance does not necessarily equal 8x transistors. And as others have already pointed out, even at 28nm you're gonna be hard pressed to see something like a GTX580 in a console. Too much powa.