undervolting is also the same it limit how much voltage the card will use, which mean indirectly limit the current that the gpu can use
the difference is that you can be more precise, with undervolting
Undervolt is NOT THE SAME.
Chips as a general rule are more EFFICIENT at lower voltages, as long as they can do the work at all.
Take a good look at the spec sheet on the BM1385 sometimes, for a prime example with actual numbers.
Ability to mine ETH for a profit has a few variables involved - MH/Watt of your SYSTEM, cost of electric, diff, etc - it's not a given that everyone will be able to mine it profitably for a year, in fact it's looking like it might achieve UNprofitable for most folks well before the end of the year (those in VERY VERY cheap electric areas have a lot more leeway).
I do expect the rate of diff increases to slow eventually as more folks get to "unprofitable" on some of their rigs and point them at other things, and folks start realising they aren't going to be able to make anything on new builds in most areas.
Oh, and the final verdict on the 1070/1080 for ETH is "not a lot of effect, too much money for the efficiency and hashrate" - but the jury is still out on other stuff - FoldCoin in particular can probably benefit a lot from the 1080 and somewhat less from the 1070 for example.
