We have measured the noise output of the cards with the help of a sonometer placed 5 cm away from the fan, with all the other fans stopped the at the moment of the measurement.
Reasonably silent at rest, the Radeon HD 4870 X2 turns out to be—not surprisingly—quite noisy when in use, right from the time that its fan starts spinning up. On the other hand, we also want to note that while the GeForce GTX 280 is pretty noisy at rest, it is much more bearable than it used to be under load.
Although the Catalyst Control Center permits us to directly augment the frequencies of the GPU and RAM, it also limits their values to 11% at best—800 MHz for the GPU (as opposed to 750 MHz at its stock setting) and 1,000 MHz for the RAM (as opposed to 900 MHz). It is possible to override this via third-party overclocking software.
Not that you’d want to, though. Even at 800 MHz/1 GHz, the Radeon HD 4870 X2 not only failed to demonstrate palpable performance gains, but it also showed a slight slide in performance. You’ll just have to take solace in the fact that you’re already running the fastest card available.