It seems that your definition of efficiency is heavily lopsided. My understanding of efficiency is entirely economic, i.e. I don't care about power consumption and hashrates as such. All I care is the balance of costs and revenues. In other words, the miner that incurs less cost and brings in more revenue is more efficient (i.e. does more with less) than the one that does the opposite...
That's what all technical parameters ultimately boil down to
my definition is different, talking about the initial investment as efficiency is a no-sense, the efficiency is only related to consumption, and the s7 consume half of the s5, so x2 efficiency
The problem is it doesn't in the least guarantee that with an s7 you will profit twice as much as with an s5 given only its half as much power consumption. Initial investment (aka capital expenditure) as a part of fixed costs defines your break-even point. You still have to shell out on the equipment first, whether you love it or not. Your personal opinion (lol) that you can sell your miner is not related to this, and I highly doubt that you will get for it the same price which you bought it at after a few months of operation (and more so before the halving)...
Even if you
personally will be lucky to sell your device at its original price tag
in fact the profit is much higher than a s5, becuse you need also more psu for the s5 since it consume more
i've done the math about it and it was highly in favor of the s7
the fact that it cost more, does not mean anything, you can always sell it for the same value even after many months, guaranteed
If the equipment still brings in cash, it makes no sense economically to sell it (prior to break-even at least). Otherwise, you would be better off by
not buying it in the first place (all other things being equal). But if it stops bringing in enough revenue at some point (negative cash flow), you won't be able to profitably sell it...
If only out of pure luck to some goof, lol
it's a strategy used to reach roi faster nothing else, there is a big part of trading in mining as well, it's not mining only, anymore
you can actually be lucky and sell above the market price with new equipments, there are cases of this happened already in the mining section
because there is a high demand for new asic