The VRMs on the powercolor are not actively cooled having no contact with the heatsink on the heatpipe assembly, but the heatsink grills are open which allows the airflow from the second fan directly on them, that being said, at stock speeds they get to about 68-69c when the core is about 56c with the fan actively blowing across them. With no contact between your waterblock and the vrms they would overheat for sure. You need to get a block that sits on them. Being that quite a few other brands have the heatpipe assembly actively cooling with heatsink contact on the vrms, you should be able to get a block, or modify one to actively cool the vrm modules. Keep in mind that these cards can draw over 300w when doing high clocks and voltages, thats alot of vrm heat.
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kind regards