IT'S OVER, AMD IS FINISHED & BANKRUPT
Polaris isn't the codename of one GPU.
One of new 14nm dies will be paired with GDDR5, and is a entry level part, the other is more mid range which will have HBM. A single module of HBM2 provides 256GB/s so two of them would be total overkill in bandwidth for a mid range card.
I'd put money on it performing around a 7970 while consuming 150w~
Its important to remember that AMD just launched their Fiji based GPUs, so they're not going to sell anything to replace them until the get a substantial ROI and sell off the majority of their inventory.
according to samsung, cards with 4x HBM stacks will be targeting 16GB
Get with the times.
AMD was the principle party behind GDDR5 too, prior to being acquired by AMD ATI was the designer of GDDR3.
AMD/ATI has controlled the path of graphics memory since dedicated graphics memory was a thing. They only produce open standards.