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 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.
I talked with nvidia developer with many back and forth messages and the result of the 41 msg conversation is:
Hi tytanick,
Below is the response from Engineering team -
Weve confirmed that the performance drop is due to the size of the DAG exceeding the total on-chip TLB capacity on the Pascal GPU. As a result, there is an increased number of TLB misses, which affects performance. Because the TLB is a fixed capacity hardware resource, and the ETH algorithm accesses the DAG randomly, we dont believe there are any software optimizations that could reduce the TLB miss rate.
In the Volta generation, TLB coverage was increased by 4x, and large DAG sizes (up to ~8GB, which wont be reached for many years) will still fit in the on-chip TLB. So these newer GPUs (Volta and beyond) will show much less performance sensitivity due to DAG size.