Power, Heat, And Efficiency
In today’s test, the liquid cooling system was powered by the platform, pulling around 12 W continuously (18 W at most). Hot cards consume more energy, and that helps explain why the LCS AXR9 290X uses less power, even with the extra cooling parts added to system load.
With AMD’s target temperature of 94 °C, full-load temperatures don’t mean much for air-cooled cards. This chart only indicates an ambient temperature of 18.5 to 19.4 degrees, where I’ve already noted the 18-19 °C temperature as a potential consistency issue.
Temperatures for the liquid-cooled card are exceptionally low. And PowerColor's solution, on its own, pulls around 30 W less as a result (though it gives some of that efficiency back to power the pump).
Now that AMD is overriding the Quiet firmware settings in its driver, it makes less sense that the air-cooled card would still run faster using the Uber firmware (particularly since the Uber setting merely allows faster fan speeds). Even more testing suggested that the source of the added performance was a 0.5° drop in room temperature! It's almost impossible to maintain a workspace with a tighter thermal tolerance, and it's pretty telling that these Hawaii-based boards are so sensitive.
The only performance gains that do make clear sense happen to the LCS AXR9 290X. It always runs cool enough to maintain AMD's peak clock rate ceiling, and rarely encounters a taxing enough load to trigger throttling. Shipping with its BIOS selector set to AMD’s default for air-cooled boards, the PowerColor card picks up a 60 MHz-higher core clock and 100 MHz-faster memory after enabling Uber mode.
Posting greater performance and lower power consumption, the liquid-cooled LCS AXR9 290X naturally achieves better energy efficiency. The reference-class Radeon R9 290X is so inconsistent (in both power and performance measurements) that I no longer wish to use it for any testing purposes, at least at its default fan settings. The only way to make the stock card perform consistently is to push its fan fast enough to maintain consistent clock rates. Of course, then it no longer behaves the way it shipped out from the factory.