What type of RAM you have on your cards, Samsung or other?
For my MSI Aero 1060 6gb with Samsung, these were the afterburner settings and the averaged results. The power limit apparently differ from maker to maker. Some get good results with 50%. It seems that underpowering decrease the hash rate quite a bit with everything else the same. On the other hand, once the card reached its max, giving more power has no further effect. For me, playing with the core speed had no effet pro or con, however, I'm doing Eth only mining. ~950 mem speed, the cards go over 25. However, you can start to experience issues on the long run.

Power|	Core|	Mem|	Avg Hasrate
50	|-200|	000|	18,8
54	|-200|	000|	19,7
58	|-200|	000|	19,7
62	|-200|	000|	19,8
50	|-200|	300|	18,1
54	|-200|	300|	20,9
58	|-200|	300|	21,3
62	|-200|	300|	21,4
66	|-200|	300|	21,4
50	|-200|	600|	17,6
54	|-200|	600|	20,3
58	|-200|	600|	22,7
62	|-200|	600|	23,1
66	|-200|	600|	23,1
50	|-200|	900|	17,0
54	|-200|	900|	19,9
58	|-200|	900|	22,3
62	|-200|	900|	24,6
66	|-200|	900|	24,8
70	|-200|	900|	24,7
70	|0000|	900|	24,7
70	|+200|	900|	24,7
62	|-200|	910|	24,6
63	|-200|	910|	24,6
64	|-200|	910|	24,7
65	|-200|	910|	24,8
66	|-200|	910|	24,8