Make sure your card is in p state 0.
It is, but p-state only affects memory clock and since x16r is irresponsive to it I doubt running P2 will make a difference even at -500MHz in AB which will make it 4000Mhz or so. At least I tried running 5500Mhz with GTX1080 and results were the same as with 4500Mhz.
Sorry your right that's true for 1080. Makes a big difference on other cards for gpu intensive algos.