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Power consumption
We measured system power consumption, sans monitor and speakers, at the wall outlet using a Watts Up Pro power meter. Readings were taken at idle and under a load consisting of a Cinebench 11.5 render alongside the rthdribl HDR lighting demo. We tested with Windows 7's High Performance and Balanced power plans.

The Asus and MSI mobos have handy BIOS switches (dubbed EPU and APS, respectively) that enable advanced power-saving features. Gigabyte has similar power-saving mojo, but it requires a separate Windows application (DES). We tested each board with its extra power-saving capabilities enabled and disabled.

The 990FX systems draw more power than our collection of Sandy Bridge competitors both at idle and under load. Between the two AMD mobos, the Sabertooth has a substantial power-efficiency advantage. The Asus consumes about 20W less than the MSI at idle, and the delta between the two is even larger under load. Switch both into high-performance mode, and the GD80 really starts sucking power at idle. So much for the supposedly superior power efficiency of MSI's fancy-pants electrical components.

Interestingly, the APS and EPU power-saving features have a similar effect on the power drawn by the 990FX systems. In both cases, power consumption falls by modest but measurable margins at idle and under load.

Overclocking
With the Sabertooth 990FX and 990FX-GD80, processors can be overclocked by raising the motherboard's base clock speed, increasing the multiplier on unlocked Black Edition CPUs, or combining both approaches. Alternatively, you can leave the whole process in the hands of the auto-overclocking intelligence Asus and MSI have imparted on their respective boards. To keep things focused on the motherboards, we let each one try its hand at overclocking our Phenom II X6 1090T. Next, we dialed back the CPU and memory multipliers to see how high the motherboard's base clock would go with the processor and DIMMs taken out of the equation.

After hitting the handy OC Genie button on the 990FX-GD80, the board booted up at 3.44GHz with a 16X CPU multiplier and a 215MHz base clock speed. CPU-Z listed a CPU voltage of 1.42V, and the system didn't so much as hiccup under a six-way Prime95 load combined with the rthdribl HDR lighting demo. Of course, it was running only 240MHz faster than stock.

Our manual run at the base clock squeezed 255MHz from the board without any extra voltage. CPU-Z reported a CPU voltage of 1.35V this time around, but no amount of additional juice would coax the GD80 to POST with a 260MHz base clock.

The Sabertooth's built-in overclocker proved to be much more aggressive than the GD80's. This so-called OC Tuner settled on a 232MHz base clock speed that pushed the CPU to over 3.7GHz with its default multiplier. According to CPU-Z, the processor needed just 1.37V to maintain this speed, which it did with the same stress test we used on the MSI board.

When we took matters into our own hands, the base clock sailed up to 280MHz with ease. We didn't have to touch the CPU voltage, which CPU-Z reported as 1.3V. The system made it all the way into Windows with a 285MHz base clock. However, Prime95 consistently spit out errors on at least one of the CPU cores, and bumping various voltages didn't alleviate the issue.