I would try to get a used GTX 1060. The cheaper, the better. The more you spent on the card, the longer it will take until you reach the ROI.
As clock rate is irrelevant, the cheap models are fine as you do not need to overclock and hence do not need best colling solution.
Which RAM is used is just luck. Even on check cards from Palit and PNY you can have Samsung chips. Most 1060 seem to have Samsung chips.
since there are no used cards available here, i have to get the new ones, so i thought ill give 20 bucks more fore better Gaming version than the cheapest Armor because it will sell better later(everyone will have cheapest versions for sell, and ill have a bit better

), and also cooling will be no problem and fans will last longer..
Also with new cards, if the memory isnt right i can return them

i am actually selling my RX480/470 rig to get the 1060s, it will cost me the same for same hashrate (ETH), 1 1060 more then RX rig.
but i will be ready for ETH drop in a month(because of those DAG epochs 140+), and 1060s 6G will sell better to gamers and will be worth more than RX 4G at that point
i will also be able to mine ZEC, im just not sure if RX have more alternative altcoins to mine than the NV?