I tweaked my GTX 1070 like this, as suggested by user "Shoo" in a comment here: http://wccftech.com/ethereum-mining-gpu-performance-roundup/

70 % Power
-200 MHz GPU clock
4450 Mhz memory clock
Fan: 55-65 % (depending on temp)

Result are nearly as good as before with less power consumption. I will measure off the wall wattage soon and post it here.