We measured system power consumption, sans monitor and speakers, at the wall outlet using a Watts Up Pro power meter. Power consumption was measured at idle and under a load consisting of a multi-threaded Cinebench 10 render running in parallel with the "rthdribl" high dynamic range lighting demo. Results that fall under "No power management" were obtained with Windows Vista running in high-performance mode, while those with power management enabled were taken with Vista in its balanced performance mode.
MSI's X58-based motherboards come with GreenPower software that lowers several system voltages by a smidgen to save power. We tested those boards with and without GreenPower enabled since, unlike some other power-saving schemes we've seen, it doesn't impede system performance by lowering or otherwise capping clock speeds.
And wouldn't you know, GreenPower is good for a few watts saved. The X58 Platinum doesn't really need the help, though. Even without GreenPower enabled, the Platinum consumes less power than the EX58-UD3R and the P6T. The differences amount to about ten watts under load, with the Gigabyte board proving slightly more frugal than the Asus.
Although the Core i7-965 Extreme offers an unlocked upper multiplier that makes overclocking a breeze, you can't increase the CPU multiplier on more affordable i7-920 and 940 models. To overclock those chips, one must increase the system's base clock speed, which runs at 133MHz by default. Think of this as old-school front-side bus overclocking, but with the base clock replacing the FSB.
To see how high we could get the base clock running on each board, we dropped our Core i7-920's processor multiplier to 12Xits lowest valueand started turning up the base clock. We also dropped the memory multiplier to 6X to take our DIMMs out of the equation. The OCZ modules we used for testing are good for up to 1600MHz. With a 6X memory multiplier, that gives us base clock headroom up to 266MHz.
Since the Core i7 likes to overclock itself when thermals permit, we disabled the processor's "turbo" mode to keep variability to a minimum. We tested each base clock speed step for stability with a punishing eight-way Prime95 load.
Our quest for higher base clock speeds began with the X58 Platinum, which started running into problems when we hit 160MHz. At that speed, the board would crash on the way to Windows, even with its QPI link set to slow mode. We tried bumping up the voltage for the processor, its uncore components, and even the north bridge, and finally got the system stable with a 165MHz base clock. 170MHz spit out Prime95 errors almost instantly, though, and no amount of gentle coaxing seemed to help.
Overclocking the P6T proved much easier. The board effortlessly sailed up to a 200MHz base clock without additional voltage, QPI tweaks, or other meddling. At 210MHz, however, it failed to boot into Windows. Posting wasn't a problem, but even with additional voltage applied all around, the P6T would blue-screen or otherwise hang before we were greeted by the Vista desktop.
A 200MHz base clock is nothing to sneeze at, especially since the P6T hit the mark with default voltages and without the aid of a "slow mode" QPI linknot that we had a choice on the QPI front. The P6T's BIOS lacks QPI link speed control, which is why, in the screenshot above, you can see the interconnect running at a much higher speed than on the EX58-UD3R.
Like the P6T, the UD3R scaled up to a 200MHz base clock without issue. We didn't need to apply extra voltage or touch the QPI link speed. 210MHz, however, proved a little more demanding. At that speed, we had to put the QuickPath Interconnect in slow mode and raise the processor voltage by a touch to get the system stable under load. Adding voltage didn't enable us to hit 220MHz, though. The board wouldn't even POST at that speed.
To put these base clock speeds in perspective, consider what they'll do for a Core i7-920 with a 20X multiplier. The X58 Platinum's 165MHz base clock would yield a core clock speed of 3.3GHz, while the P6T's 200MHz would take you up to 4GHz. An extra 10MHz from the UD3R's base clock would net a 4.2GHz processor clock on the Gigabyte boardif your i7-920 were so inclined, of course. As is always the case with overclocking, your mileage may vary.