I got an Asus ROG Strix GTX 1080 yesterday and just finished popping it into my main desktop - it's supposed to go into a dedicated mining rig but I, uh, didn't notice that it has both 6 and 8 pin PCIe power connectors...
Anyway, after doing the DDU and driver dance I'm getting about 1278 with -i 5, -c 4, no core overclock (because it is o/c'ed to begin with) and mem overclock the same as my 1080 FE (4811 MHz); which, btw, is still running at around 1220 for >24 hours continuously now.
Interesting tidbit: I started off at -i 4 because I didn't want desktop interactivity to be impaired - the other machine with the 1080 FE in it is damn near unusable because the mouse/display responds so sluggishly - but this proved to be a non-issue, and the lower intensity cut the hashrate by ~150 (and lowered power draw reported by hsrminer by a mere 4W, from 163 to 159). Oh, and this computer is also mining a Cryptonight coin with the CPU... Ryzen kicks ass, is all I'll say about that.
EDIT - so the new GTX 1080 - without any core overclocking at all - is doing the same thing where hashrate drops off by a good 100-150; it took about 3 hours in this case so I guess I need to *underclock* the core to get it to work with this miner...