what you are failing to factor in is the 580s are beasts at dual mining , if you have adequate cooling a good 580 can do 30mhs eth and 95 lbr for 150 watt
that 95 lbry is basically nearly 3 times what i can get out of a 1070
A GTX 1070 should be good for more than 300 MHash on lbry - if you're seeing only 30 you're running some really badly outdated software, or have something configured WAY wrong.
Sure you're not confusing ETH hashrate on a 1070 (which IS in the 30 Mhash ballpark) with lbry hashrate?
On the other hand, ETH isn't a good choice for the 1070 any more, since RX 470/480/570/580 pricing dropped back under the $400 range.
The reason to get a 1070 is for OTHER algorithms like the one used by ZEC/ZEN/ZCL/BTG, where it IS comparable to superior on hash/$ to the RX series cards, or lyra2r2 where it blows away AMD on hash/$ - among many other options.
Keep in mind that ETH is not the end-all or be-all for GPU mining - it's the biggest SINGLE GPU-mineable coin right now, but not the ONLY profitable one by a long shot and often not the most profitable on a income/cost of rig basis.
