Probably your GTX 1060 cards have Hynix memory. I don't know the reason but they give very bad performance. Three of my GTX 1060 cards have micron memory and their hash rate is around 24-25 MH/s. One of my cards has Hynix memory. Its hash rate is around 17-18 MH/s.
Nvidia 1060 cards will be given around 21MH for mining ethereum and as your said according to the ingrated RAM on the cards you can find the profit and difference. If you samsung ram that will give you better performance than the regular one.
I am mining ethhash algorithm via perfectmine. I did not get the same amount MH as you confirmed here.
Maximum amount of hash for the cards you are having will be giving around 22 MH maximum. I am saying that I am getting this hash power without overclocked the card.