I don't know much about Vega except it will be using HBM2. It could be a "big" die, but could also be 2 dies on a interposer. The reason I suggest this is that Raja told Ryan at PCper, in an interview a couple of month ago that AMD won't do big dies anymore, because of economics and time to market. Now... If you going to make use of all that bandwith HBM2 offers, it makes no sense to use it on a medium sized chip. So, either a semi-big chip at maybe 350-400 mm2, or two medium chips paired together. I really hope for the first alternative.