thank you guys for all answers! really 

in this moment i'm using a mod bios from anorak.tech specific for my Rx 570 4gb (113-2E366FU-053) power safe with msi ab:
mv -93
core clock 900
memory clock 2100
fan 55%
temp. 41c
ethereum mhs 19 solo mode

and a rx570 8gb (113-2E366AU-X56) also modded
mv -93
core clock 900
memory clock 2100
fan 55%
temp. 41c
ethereum mhs 19 solo mode

800watt at the wall for only 38 mhs
 
now i ddu all drivers and try AMD blockchain driver (latest 23th august right?)

after this i try  -cvddc 875 in bat