Legit Reviews posted a review on the Ethereum Hashrate Performance Drop Might Be Coming - AMD and NVIDIA GPUs Tested A quote from the article:

If you are mining Ethereum you might have noticed that your hashrate recently dropped if you are using AMD Radeon RX 400/500 series cards. Seeing your mining hashrate drop is nothing new for Ether miners and it is usually due to the growing DAG file size. When the move to DAG epoch #130 happened it seems that the AMD Radeon 400/500 series cards took a performance hit while the NVIDIA GeForce GTX 1000 series cards and older AMD Radeon 200/300 series cards did not. Let's take a look at some NVIDIA and AMD video cards and see what will happen months down the road at future DAG sizes.

 Ethereum Hashrate Performance Drop Might Be Coming - AMD and NVIDIA GPUs Tested @ Legit Reviews