If mining ETH, GTX 1070 gets 31MH/s while 1060 gets 23MH/s. The 3GB 1060 is half the cost of the 1070 while producing 75% the hashrate. Do you not consider the 3GB 1060 a good choice because it will become obsolete due to only 3GB vram? It seems like the next best thing to an RX 570 for mining RIGHT NOW. They can always be sold when the vram becomes too small to mine.
1070s mining eth at 31 mh/s sounds good to me!
I was focused on 8gb assuming I would be able to resell easier and that the 8gb would offer better overall ROI but again I'm so fricken new and at this point I'm really just itching to build another rig. Perhaps 4gb would be fine, not sure about 3gb or if that's a great investment at this point. Don't want the rig being obsolete as you mentioned any time soon