On all GTX 1070/1080 cards you will need to keep increasing core a little with each epoch change or it will keep dropping hashrate, it will no longer be as high as what it used to be back in the days. Its caused by a driver bug that nvidia will not fix.
The question is if all nvidia will gpus will have the same fate with the dag file because even if eth is gone then will be other coins with the dag. That makes new nvidia gpus less attractive because you dont know when they will have lower hashrates every few days.