Temps and power-draw
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Leaving the fan-speed to auto results in it spinning to 2,500rpm, as noted earlier. The basic card isn't the quietest around, so adding to the noise is one side-effect of raising voltages.
The faster fan struggles in keeping the GPU cool, clearly.
Power-draw
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Increasing the engine voltage leads to a higher (system-wide) power-draw, by around 10W. That's pretty much acceptable.
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Whilst we can rationalise the idle power-draw readings, the same bump in core voltage - 1.287V from 1.125V - has a huge effect on under-load power-draw.
We ran the test multiple times and found the result to be consistent. Running the card in its factory-default state returns a power-draw figure of 178W, which is still some 13W higher than the Sapphire card.
The near-50W increase over a vanilla HD 5770 erodes much of the power-efficiency goodness that's implicit to the Juniper GPUs.