well, I believe something wrong with a figures here
look, I have 1070 with Micron memory on it. everyone know this memory on nv cards sucks.
it overclock to 8000-8500 Mhz only. and even with this clocks my cards was able to deliver about 30-30.5Mh/s on eth
so if your 1080 has a samsung memory so it could reach even higher speed, the trick here is not overclock the core - the memory only!