Power consumption
We took our power readings at the wall outlet using an Extech 380803 power meter. The "idle" readings were taken at the Windows desktop, while the "load" readings were taken using SMPOV and the 64-bit version of the POV-Ray renderer to load up the CPUs. In all cases, we asked SMPOV to use the same number of threads as there were CPU front ends in Task Manager—so four for the Extreme Edition 965, two for the Athlon 64 X2, and so on. The test rigs were all equipped with OCZ GameXStream 700 W power supply units.

The graphs below have results for "power management" and "no power management." That deserves some explanation. By "power management," we mean SpeedStep or Cool'n'Quiet. In the case of the Pentium XE 965, the C1E halt state is always active, even in the "no power management" tests.

The tricky part about these tests is getting good numbers for our "simulated" CPU speed grades. In order to make it work, you have to set the proper CPU core voltage, not just the right clock speeds. I made an attempt at simulating the Athlon 64 X2 4800+ and 4200+ on Socket AM2 and the Pentium D 950/960 by setting the CPU voltages manually, but I've put an asterisk next to those CPUs in our results as a reminder that they're simulated.

For the Athlon 64 X2 4800+, I set the voltage at 1.35 V. The X2 4200+ was set to 1.3 V. The "power management" idle scores were simply taken from chips with the same cache size (the FX-62 and 5000+, respectively), because all of these processors share the same 1 GHz/1.1 V idle with Cool'n'Quiet.

The Pentium D 950 and 960 were trickier, since each Pentium D's voltage needs are programmed at the factory. In this case, I stuck with the default of 1.312 V for both speed grades. On an 800 MHz bus, the Pentium D 950 and 950 both clocked down to 2.4 GHz at idle via the C1E halt mechanism. The Extreme Edition 965 clocked down to 3.2 GHz at idle.

The Socket AM2 systems unequivocally use the least power at idle, but under load, the story changes a bit. The battle between 939 and AM2 appears to be kind of a wash with the CPUs going full tilt, and the X2 4200+ on Socket 939 actually uses less power than the AM2 system. Most jarringly, the FX-62 eclipses the Pentiums when it comes to power use under load. 230 watts for the whole system isn't horrible, but Intel's chips are much more frugal with power than in the past.