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There is no 1.5 times decrease in consumption there. I watched the tests of cards 1070 devour 180 watts at 460sol well old 280x with the optimization of 185-190watt
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You compare not optimized 1070 with optimized 280x. In tests I reached about 210-220W power consumption from GTX1070 on Neoscrypt, but it's not optimal
To get 460sol/s from GTX1070 it could tuned at 140W consumption.
The simple example:
28 nm GTX970 gives 290 sol/s at 140W (OC, DV)
16 nm GTX1070 gives 450 sol/s at the same 140W (OC, DV)