"gpu-memclock" : "1600"
Why 1600? Try 1500, or 1250. You might also want to play with gpu clock, going down from 1085 may increase the hashrate.
i really dont know know why 1600.. i try 1000 1500 but no luck ... get worse hash rate actually 270khs...
the 1085 seems neceesary if i go lower than that i can worse hash rates but ill try changing the memclock maybe i better hash rate