When we tested the DL-360G5 late in the series after having difficulties with the HP DL-160G5's Windows testing, we found it behaved similarly to the Dell 1950 (which has the same number of CPUs as this bigger HP box), consuming the highest number of watts, but also doing so with the largest number of drives.
Microsoft, Red Hat and Novell/SUSE each have power savings and green initiatives that are widely publicized. Nonetheless, we were astounded by the effort we needed to undertake in order to chase down of firmware, BIOS and other updates was necessary to get real savings in the tests we conducted. Tuning servers for optimized power savings could yield better results, but would create a new painstakingly tedious server management discipline required to constantly control the deep complexities of the configuration variables involved.
We recommend that every potentially green server deployment be thoroughly checked, as each server model may or may not have the necessary BIOS settings and operating system chipset recognition features that will result in a power savings. While all of this leg work might ring true to that famous line in the Kermit the Frog song, entitled "It Ain't Easy Bein' Green", if you consider the power savings over a five year service life, the boost to the bottom line will likely be worth the effort.
Henderson is principal researcher and Dvorak is a researcher for ExtremeLabs in Indianapolis. They can be reached at email@example.com.