You guys both mention 470-s to buy if we talk about eth. 1* GTX1070 can do about 27 MH/s or even 30. Then 4* 1070 can do about 120 MH/s Eth and we have 6* RX580 in same price range but they can do about 160-180 MH/s. Why should I even think about 1070-s? I don't get it.

470 takes less power than 570 and 580? Why 470 is good option?
I'm really confused. As beginner I thought about 570 or 580 because they are newer models(bigger power bills??) and maybe easier to sell gamers if mining world collapse.

Ofc. there can be availability issues. I would like to have backup option. Mixing different cards in same rig is not good option because of drivers issues?