I've got a Vega 56 with Airblow cooler from Gigabyte, after SoftPowerPlayTable mod and same settings as below on win10 with blockchain driver, I can reach only 1350 h/s at 150W with xmr-stak but aftersome time it drop at 1160h/s.
Cannot get more, probably because lack of ram? I've got only 4gb ram, but i'm running a mixed system with also 5 Nvidia that mining well.
Any advice?

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Wattman Settings (Blockchain Beta driver):
-30% GPU Frequency;
950 HBM Frequency;
Fans at 3500 - MAX (Ignore core thermals. What you need is to have the memory below 70º to keep the high hash rate. An undervolted gpu will be fresh enough to not auto raise the blower speed, hence not cooling the memory. At 25ºC ambient temperature I needed 3500RPM set at min speed);
Power Limit -20%.

Globaldrive settings (Blockchain Beta driver):
Crossfire disabled;
HBCC on...