My 1080 Ti's say differently. If I set power limit to 60% I get around 1500MHz. If I then add +150 to the core, the core clock increases 150Mh to around 1750Mhz. Do that on 4 cards and you are effectively getting a 600Mhz boost and the results are in the MH/s the miner is reporting.

With GPU boost the freq does jump around here and there but usually not more than 50Mhz.