We now know all about stock-clocked performance. So just how much headroom does Cayman have? First on the testbench is the Radeon HD 6950. There's no voltage adjustment, so it's a case of ramping up the clocks until the card fails to complete a single loop of either Aliens vs. Predator or Just Cause 2, run at 2,560x1,600 settings. We ramp the fan-speed up to 60 per cent of maximum.
Click to enlargeHealthy rises for both the core and memory, jumping from the default 800MHz/5,000MHz to 900MHz/5,500MHz without issue. That's over 10 per cent on both lines.
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Switching cards and putting the HD 6970 on the rack, the card tops out at 948MHz core and 5,800MHz memory - representing a slightly lower jump in percentages above stock.
Here's how the overclocked cards play out in the two above-mentioned games:
The overclocked HD 6950 is able to almost catch the stock HD 6970 - the lack of shaders and texture units compromising higher frequencies - while the overclocked HD 6970 gets closer to GTX 580.
Just Cause 2 is more partial to frequency changes, as the HD 6950 OC just about overtakes the bone-stock HD 6970. What we can say is that AMD will not regain the single-GPU crown with pre-overclocked HD 6970s; GTX 580 is just too far ahead.