Where did you see that the x80 will use GDDR5X?
From the article.
NVIDIA GeForce GTX 1080 Features GDDR5X and GeForce GTX 1070 Features GDDR5 DRAM
Rest of the board was not pictured but the specific SKU was pictured with a total of eight 8 Gbps memory chips featuring 8 Gb density. The board uses the latest Samsung K4G80325FB-HC25 chips which use the 8 Gb DRAM and run at 8 Gbps speeds. This will allow NVIDIA to boost not only the bandwidth but also the VRAM size on their upcoming GeForce cards.
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We know that the GP104-200-A1 SKU will be featured on the GeForce GTX 1070 graphics card featuring GDDR5 memory while the GeForce GTX 1080 graphics card will feature GDDR5X memory. It is pointed that both GDDR5 and GDDR5X memory are not pin-to-pin compatible since GDDR5 uses a 170 pin ball grid while GDDR5X uses a 190 pin ball grid layout. Both cards feature the same amount of VRAM of 8 GB but 1080 will have higher total bandwidth available up to 384 GB/s while retaining a 256-bit memory bus.