For some reason AMD has started locking the overclocking potential of its graphics cards with a BIOS method that limits all software overclocking applications to a pre-determined frequency. This was the case with the Radeon HD 5450 and 5570 boards that we reviewed recently. The latter could desperately use a little tweaking, yet AMD limited the core to a max clock of 700MHz -- at least in our sample anyway.
This is unfortunate and takes a great deal of value away from the Radeon HD 5570, as we imagine its core would easily reach 800MHz without much trouble. While testing the Radeon HD 5830 we encountered the same overclocking limitations but with a broader headroom, which allowed us to increase the core frequency by 100MHz, while the memory got a 300MHz bump. This mild overclock helped boost performance by a respectable margin.
The overclocked Radeon HD 5830 was able to match the GeForce GTX 285 in Company of Heroes, boosting the average frame rate results by 12% to 56fps. Then with S.T.A.L.K.E.R we saw a 17% performance increase, which actually allowed the Radeon HD 5830 to overtake the 5850.