1080's have a tiny bit better than 1070 Ti's?
If you aim for max efficiency, 1070 ti will at least match and usually beat 1080 hashrate in the 100-110 watt power range at the same power usage.
This depends on the card model and sometimes the specific card, I've only seen ONE match situation on "same model" cards, my Zotac Mini 1080 vs my Zotac Mini 1070 ti - but that's a case of the 1080 Mini I have being THE BEST 1080 I have in that power range by a bit.
If you push for higher hashrates at the cost of efficiency, the 1080 starts outhashing the 1070 ti typically around 120-125 watt level but never outhashes a same-model 1070 ti by the common 10% cost differential, presuming same power level on each card.
*IF* you can get a "same model" 1080 for the same price or within 2-3 % of a 1070ti, it's probably worth doing IMO - otherwise no.
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