Guys,
Here's a fix for the 4850 temperature issues. I found it at:  http://forums.guru3d.com/showthread.php?t=265745
Copied from the page:
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if you make a profile in catalyst after turning on Overdrive( make sure clock and memory settings are correct). You can then go to the file "C:\Users\Bretware\AppData\Local\ATI\ACE\Bretware. XML. the xml file will have the same name as the catalyst profile you saved. right click and hit edit.

<Feature name="FanSpeedAlgorithm_0">
<Property name="FanSpeedAlgorithm" value="Manual" />
</Feature>
<Feature name="FanSpeedRPMTarget_0">
<Property name="Want" value="0" />
</Feature>
<Feature name="FanSpeedPercentTarget_0">
<Property name="Want" value="65" />

Change the value to "manual" and Want value to "65"

Save the file then reload your profile in catalyst.
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The problem with the 4850 is that the stock fan is locked at like 22% or something.

This mod seems to work for the guys on that thread. Looks good if you don't want to spend money on after market cooling mods.