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We chose Crysis 2 for our overclocking tests. In our experience, this title is extremely sensitive to variations in GPU frequency, reacting negatively when a graphics card is near its edge (even more so than FurMark).
Both the Radeon HD 7970 and 7970 GHz Edition are set to 1050, 1100, 1150, and 1175 MHz. We were unable to reach anything higher than 1175 MHz on either of our GHz Edition samples without encountering serious visual artifacts.
First, let’s compare power consumption across the four runs at each frequency setting.
As we can see, increased power consumption corresponds to a reduction in GPU voltage. We would have expected the opposite.
Starting at 1175 MHz, we began to see minor visual artifacts (missing texture transparencies and polygon errors) that we were able to remedy by increasing VDDC. Apparently, PowerTune is stepping in very early on to turn voltage down, way before power consumption actually reaches a critical level.
The results of this intervention are quite obvious, manifesting as sporadically-dropped frames, texture errors, absent light sources, and other missing effects. Strangely, although the average and maximum frame rates continually increased, the minimum frame rates started to go down with each clock rate increase starting at 1150 MHz.
Our Radeon HD 7970 GHz Edition cards aren’t any more capable than the original Radeon HD 7970 overclocked. In our opinion, you reach the best results at 1150 MHz using AMD’s own tools. Push any harder and you’ll find the card dropping frames (even if its average frame rates seem to suggest better performance).