I'm still wondering if the Pascal GP104 will be 256bit or maybe 384bit, seeing as the new top end GP100 will be HBM2.
the sensible option would be 256bit, but that would make it a direct 970/980 replacement, in the pecking order (not in performance), where as there will be no 384bit parts if the top end goes HBM2 and the next one down is 256bit.
I know that these decisions would have been made a long time ago and they could not have known that HBM2 or even the GDDR5x would not be quite as available as it would seem (according to the rumours/reports). But it seems like a good idea to utilise the 384bit for the next part down from HBM2.
It could look somewhat like this.
1080ti/TitanXI HBM2
1070/1080 384bit
1060/1060ti 256bit
1050 and below 128bit