Power consumption
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.

In testing, we discovered that the latest BIOS for the GA-P35-DQ6 motherboard we used for our P35/DDR2 system doesn't correctly throttle clock speeds with either C1E or SpeedStep. Older BIOS revisions used to work, but Gigabyte broke something with its last release. That could explain the lower CPU utilization results we saw for the P35 configuration in some of our peripheral testing.

Power consumption looks reasonable for the X38 Express. The chipset is certainly more frugal than the nForce 680i SLI. Under load, there's little difference between its power consumption in our DDR2 and DDR3 configs.

Don't pay too much attention to the higher power consumption figures for our P35/DDR3 setup. That system uses an P5K3 Deluxe motherboard that has always been rather power-hungry. Asus is aware of the issue, and they worked to address it with the P5E3 Deluxe we used in our X38/DDR3 config. As you can see, their efforts paid off.

Overclocking
For our overclocking tests, we dropped our CPU multiplier to 6X—its lowest possible value. Memory bus dividers and MCH straps were also adjusted to keep our DIMMs running well within their limits at overclocked front-side bus speeds. Next, we turned our attention to the front-side bus, cranking it up and using a combined load of Prime95 and the rthdribl HDR lighting demo to test stability along the way.

With the GA-X38-DQ6, we sailed easily up to a 500MHz front-side bus without the need for extra voltage. 510MHz refused to POST, though, and no amount of voltage manipulation, sweet talking, or other tweaking could coax more than 500MHz from the board.

Like the Gigabyte board, the Asus flew up to 500MHz without issue. Booting at 510MHz required a little extra CPU voltage, but that was it. However, 520MHz wasn't in the cards. We tried fiddling with voltages, adding the board's optional chipset coolers, and even a gentle massage, but our P5E3 refused to boot with a 520MHz front-side bus.

Front-side bus speeds in the 500-510MHz range are certainly impressive, and they suggest that both boards offer more than enough overclocking headroom for most folks. However, we've had a number of P35 Express boards up to a hiccup-free 490MHz front-side bus, suggesting that the X38 doesn't have a distinct advantage when it comes to overclocking headroom.

As is always the case with overclocking, your mileage may vary.