I have had my 1080 ftw card for some months.
Even after setting to the slave bios to get 130% power target I noticed some throttling issues.

I have a custom loop with two 480mm rads.

After reading online i discovered that gpu boost 3.0 had a scaling system of mhz to voltage. If you increase that voltage to 100% in overclocking programs that increases your highest clock gpu boost can reach.
Power limit to 130% is fine.

Memory however is the killer here I think most cards can get +500 on the memory but this is a bad thing.
You will go over the power limit and become power limit throttled. In benchmarks this is 5-7 fps on average lost as the memory takes away power from the core.

With voltage +100
Power limit 130%
Core clock +120
I hit a stable core clock of 2132

However if I drop my memory to +461 I just go under power limit and my fps jump up 5-7fps.
In benchmarks or games it shows. Afterburner has power limit and voltage limit. Turn them on keep it under those limits under the edge squeeze every drop out.