Both GTX 1060 9Gbps and GTX 1080 11Gbsp are using new versions of GP106 and GP104 chips.
First benchmark is MSI GeForce GTX 1080 GAMING X PLUS
Gigabyte, Asus, EVGA, Inno3D and the usual have announced the cards today as well so more benchmarks coming soon probably.
The GPU is clocked at 1.683 MHz with a 1.823 MHz boost at default clocks. This is 100% similar to the regular Gaming X model. However the effective memory data-rate was bumped up from 10.000 MHz towards 11.000 MHz (effective data-rate). Precisely that increase offers the PLUS model 10% more memory bandwidth. And yes the GeForce GTX 1080 very much so likes more graphics memory bandwidth.
Quite honestly I did not expect a card with slightly faster graphics memory to make this much of a difference performance wise. On a relative scale, everything is just that, ... relative. As seen from the regular Gaming X model I doubt you're going to notice a few FPS more. But the fact remains that just that 10% faster memory is responsible for an extra 4% in gaming performance (compared to the standard Gaming X). And once we tweak that card that difference is roughly 10% faster compared to the regular Gaming X card. And when we take relativity one step further, once you compare all the way back to a reference (Founders Edition) GeForce GTX 1080 and apply a tweak, you can again up-to 20% in performance. And that certainly is interesting.
Update: PCGH have 1060 9Gbps compared to 570 and 580 in The Witcher 3: