Gddr5 is unlikely, I think. Not 8 GB of it anyway.
Stacked DDR 3 maybe ?
Anyway looks like something just doesn't add up in Durango specs.
Between bandwidth and GPU Orbis seems to have a clear advantage, sure they're still roughly in the same ballpark, but...
Idk, how much do you think GPU customization costed ? Ms had a very large team at amd working on the GPU, I would think it was worth it, or they could have saved money on r&d and used the money to cover a small initial loss from more powerful components, instead (better hardware allows you to stay on the market longer, and the longer the generation lasts the more profitable your console is in the long run).
Everything considered, I'd even go as far as claiming we...still have no idea.