Power consumption and efficiency
Our Extech 380803 power meter has the ability to log data, so we can capture power use over a span of time. The meter reads power use at the wall socket, so it incorporates power use from the entire system—the CPU, motherboard, memory, graphics solution, hard drives, and anything else plugged into the power supply unit. (We plugged the computer monitor into a separate outlet, though.) We measured how each of our test systems used power across a set time period, during which time we ran Cinebench's multithreaded rendering test.

All of the systems had their power management features (such as SpeedStep and Cool'n'Quiet) enabled during these tests via Windows Vista's "Balanced" power options profile.

Although we don't usually include "simulated" CPU speed grades in our power results, I've made an exception for the Q8200 out of sheer curiosity.

Let's slice up the data in various ways in order to better understand them. We'll start with a look at idle power, taken from the trailing edge of our test period, after all CPUs have completed the render.

The Phenom II is a major, major improvement in idle power draw over the original Phenom. As with the past generation, though, the deactivation of one of the cores on the X3 product has no measurable benefit to power consumption at idle. However, I'd say the power draw of the DDR3 system is pretty decent, considering that our Asus Socket AM3 board is a high-end mobo.

Next, we can look at peak power draw by taking an average from the ten-second span from 15 to 25 seconds into our test period, during which the processors were rendering.

Looks like DDR3 saves a few watts in peak power draw, at least. Even so, the X4 810 consumes a little more power than Intel's comparable quad-core processors. And the X3 720 draws just as much power as the X4 810. Looks like the 720's higher clock speed and larger cache are making up the difference.

Another way to gauge power efficiency is to look at total energy use over our time span. This method takes into account power use both during the render and during the idle time. We can express the result in terms of watt-seconds, also known as joules.

We can quantify efficiency even better by considering specifically the amount of energy used to render the scene. Since the different systems completed the render at different speeds, we've isolated the render period for each system. We've then computed the amount of energy used by each system to render the scene. This method should account for both power use and, to some degree, performance, because shorter render times may lead to less energy consumption.

Boy, are these last two measures close. Our simulated Q8200 uses just a little less energy to render the scene than the X4 810. Intel may have a slight edge in power efficiency, but in this product category, the Phenom II is very, very similar.