It appears as if NVIDIA has a lot of unsold GDDR5X memory chips as it now is refreshing its own unsold GP104 inventory, to make them more attractive to gamers. We first saw the GP104-based GTX 1060 6GB get the GDDR5X treatment, now it is the GTX 1070’s turn. It will receive the new memory with otherwise unchanged specifications. ZOTAC is one of the first add-in card partners that is ready with one such card, the GTX 1070 AMP Extreme Core GDDR5X (model: ZT-P10700Q-10P).
Since the only thing that is changed is the memory it sticks to a memory clock speed of 8.00 GHz, even though GDDR5X chips are rated for 10 Gbps. The card is factory-overclocked by ZOTAC with a default clock speed of 1607 MHz and a GPU Boost of 1797 MHz. This is lower than ZOTAC’s own GDDR5-based AMP Extreme card, which runs at 1805 MHz GPU Boost frequency, but also overclocked memory at 8.20 GHz.
Out of the box you really should not notice a difference in performance between a GDDR5 and GDDR5X card, but the card with GDDR5X should have significant overclocking headroom.