To get to that 2x number, that would be throwing out the early dev specs and using the latest and greatest gpu design from amd.
Now how likely they went from a four year old card to a 2012 is another topic. I was giving best case.
I've said this to you before and I'll say it again. Developing a custom GPU isn't a process of starting at one retail GPU and moving to others along the way. GPU7 (I suppose I might as well use that name now ) started based on the R700 architecture (much like the HD5xxx and HDX6xxx are ultimately based on R700) but its been customised over a period of over 3 years now. By the time it was completed it'll be a different GPU, not a R700, not a R800 or any other retail part. It also won't use the same manufacturing process obviously.