drop mem down to 1400 or so, undervolt it. my 4gb rx580's get 39-40 at 1400mhz core, 1400mhz mem. undervolted to 1075 on core, 850 on mem. about 125-130 watts. My 570 will only run up to about 1300 mhz at +50% power. If you use overdriventool copy the fastest core state and voltage to everything but slot 1 and 2.