OverclockingTo find the maximum overclock of our card we used a combination of internal AMD OC Software and our benchmarking suite. At this time no public software supports overclocking the HD 4xxx Series, other than CCC which has a limit on how far you can OC.
The final overclocks of our card are 682 MHz core (9 % overclock) and 1069 MHz Memory (8% overclock). Both overclocks are quite limited, probably AMD binned all the good overclocker GPUs away to be used on the HD 4870 cards.
When changing memory clocks I noticed that the step size (with the software I used) is 25 MHz around 1000 MHz, so you can only OC to 1000 MHz, 1025 MHz and 1050 MHz - quite a limitation. After 1050 MHz the steps become smaller again.
Under load the HD 4850 gets quite hot, but not too hot. Actually I prefer this over a card with a noisy fan. For our measurements we used the hottest of the three on-die sensors of the GPU. Due to the design of the cooler it is easy to touch a part of the hot cooler baseplate when removing the card. So after using this card wait a minute or two before you burn your fingers.