People, this is not a consumer gaming card. It's for extreme rendering and modeling. Rendering companies will make good use of this.
Not unless they're running that GDDR5 at some really insane speeds. In the 390X, the HBM memory is expected to have a bandwidth of 640GB/s. Even the base 390 is expected to push 480. Not to mention that all the new cards are going to be at least GCN 1.2 so they get the lossless color compression (ala Tonga) across the board.12 GB Gddr5 with a 384-bit will be very fast and "maybe" beat 4 GB HBM