Please note we are only using FurMark as a tool to show the overclocking problem that we encountered.
However, the problem was first noticed when benchmarking the overclocked Radeon HD 5970 in long stressful benchmarks such as S.T.A.L.K.E.R Clear Sky. In such games the overclocked Radeon HD 5970 failed to provide strong performance gains and if we looped the tests several times the results often ended up being lower than before any overclocking took place and this was because the card would throttle down to 550MHz.
AMD did make it clear that the Radeon HD 5970 does throttle down to avoid any damage when operating at high temperatures. However they also portrayed the Radeon HD 5970 as a stellar overclocker that could and would hit Radeon HD 5870 speeds. While this is true to a certain extent as the Radeon HD 5970 will reach Radeon HD 5870 frequencies, it will also throttle back after a few minutes in certain stressful games such as S.T.A.L.K.E.R.
So this is not really a practical overclock then since the card will inevitably throttle back. While it won’t happen as fast as it did in Furmark it will happen and that is the point. The Radeon HD 5970 is still a great product and it is the world’s fastest single graphics card but it is not the overclocking behemoth that AMD made it out to be. At least not with the standard cooler which they say is rated up to 400w.