I've been playing around with the new card and comparing it to my 7970s. With the exception of MW (DP) the GTX 1080 outperforms the 7970. In some cases by wide margins and in others not so much. This will at least give you some numbers for the GTX 1080 so you can compare it to whatever card you have and help you decide if a upgrade is worthwhile. The 1080 definitely performed better than my dead GTX 780 so that upgrade was worthwhile.
GTX 1080 - clock rate 1911-1965 MHz selected by card and it changed with project
7970 - clock rate 1100 MHz - selected by me
Both cards in identical I7-3930K machines with 12 threads available to the GPU.
Credits / day
COLLATZ x2 WU
1080
5.2M
7970
3.0M
PG x2 WU
1080
1.2M
7970
405k
MW x3 WU
1080
133k
7970
433k
POEM
1080
1.2M (x4 WU)
7970
600k (x3 WU)
MOO
1080
580k (x1)
1080
623k (x2)
7970
507k (x1)
GPUGrid - both cards tied at zero credits
They have to change the program to match the architecture of the new NVidia cards and they can't do that till they get one.
The number of simultaneous WU were chosen to get the cards to 100% loading.
NOTE: it is possible the GTX 1080 would perform better on a PCI 3.0 mb but you can't prove it by me
Both cards were "optimized" on Collatz.
I didn't run Asteroids or Einstein and I damn sure didn't run Seti ... I only run Seti when I need 100 hours for WuProp stars!!