We began our overclocking efforts by trying to repeat the settings from last quarter's build. Unfortunately, this combination of hardware simply didn’t work all that well at 1.40 V.
So, first we had to find the best stable clock, using eight thread of Prime95 to test each possible combination of settings.
Note that we couldn’t reach a 48x multiplier. Still trying to get close to the previous build’s 4.8 GHz, we tried increasing base clock, but continuously ran into a stability wall. Eventually we settled with 100.1 MHz. Next, we tried lower voltage.
The system wouldn’t overclock higher at less voltage, but we were able to reduce power consumption somewhat by dropping CPU core to 1.365 V. The lower core voltage also aids the processor’s survival time, even though we estimated that the same CPU could survive 1.40 V for many months, likely exceeding a year. Perhaps 1.365 V will give us multiple years of operation?
Any attempt to set timings manually failed, even after trying various memory voltage settings. XMP Profile 1 worked flawlessly, but didn’t give much room for overclocking.
Setting “CPU Load-Line Calibration” to Level 1 causes core voltage to increase slightly at high CPU loads. Lower calibration levels allow the voltage to drop under load, when it was most needed for extra stability.
AMD's Catalyst Control Center has a built-in overclocking utility that works fairly well within the limits of its Radeon HD 6970 GPU, though those limits are artificially placed and somewhat conservative. The problem is that reference-based cards have a limited range of frequencies, and software unlocking, such as the configuration file change in MSI Afterburner, simply didn’t work. We even tried the latest Afterburner version with the verbose configuration file change to no avail, instead settling for the limits of graphics driver’s built-in utility.