I researched into it and from what people are reporting it is true. 1060 gets the best increase upwards of 15-30% (like you saw) Average hash from what people were reprtong was about 29-31MH/s for a 1060. while 1070 gets about 3-5% and 1080TI gets 2%
Thats insane.. 30Mh/s from a 1060? figures after i just bought 7 1070s, 1060 are considerably cheaper then 1070 in my country..