OCC has published a new review on the PowerColor HD 4890

Overclocking the HD 4890 from Powercolor was no different than any other ATI based video card I have looked at. To make sure the HD4890 stayed as cool as possible, I increased the fan speed to 100% in the Catalyst Control Panel and was greeted with the old familiar sound that the ATI reference cooling solutions deliver at full song. But it does keep the card relatively cool to the tune of 55C under load. I then went straight to the clock speeds and started bumping up both the RV790 core and GDDR5 memory, first on the GPU core and then on the memory. I found the maximum stable speed for each sub system and then worked to find the best combination of both memory and GPU core speed. Individually, the core and memory could run slighty higher speeds but together, the best I could manage was 970MHz on the RV790 core and 1060MHz on the GDDR5 memory. This is an increase of 115MHz or roughly a 14% increase - not too shabby. Percentage wise, the memory increase is less dramatic at 85MHz or just under 9%.

PowerColor HD 4890 Review