I thought this might be useful to some - My 5850 got slightly higher than the one in the quote, 70 is the max temp you want to be aiming for, if some things dont work, lower the overclock.
Just posted this on another thread where the guy was saying that he was going to flash his bois to overclock his 5850, which i found is not nessesary for my Sapphire 5850.

I did the following:


* Reset any CCC overclock
* Download MSI Afterburner http://event.msi.com/vga/afterburner/download.htm
* Install, run it, let it read your card profile
* Go to "C:\Program Files (x86)\MSI Afterburner\Profiles"
* Open VEN_1002&DEV_6899&SUBSYS_0B001002&REV_00&BUS_1&DEV _0&FN_0.cfg with notepad
* Add/change
VT1165_Defaults = 17 33
* Save that
* Go to C:\Program Files (x86)\MSI Afterburner
* Open MSIAfterburner.cfg with notepad
* Set EnableUnofficialOverclocking to "1"
* Save that
* Restart MSI Afterburner and you should be able to run the clocks up as high as you want.
* Dont change the corevoltage, my Core is 870, Memory 1220
* Save it as a 2nd profile, leave the stocks as the first profile
* In the properties, under profiles, set the overclock as the 3D profile, and set the stock and the 2D profile, this way it's not always running your overclock
* In the settings enable the fan user defined software control, and mine is set at the following: 20%:40C 50%:50C (set the fan speed so your card doesnt overheat)
* Also in the properties, start it with windows, and start minimized

Run FurMark to test stability/temps for 10-15mins (doesnt have to be fullscreen, 1024x768 is fine) http://www.ozone3d.net/benchmarks/fur/

Right now i have my 5850 at 870/1220 (stock was 725/1000, new clocks are past 5870 stock), its running at ~50C on full load during games. Works awesome.

Q6600 @ 3.2ghz
4gb ram
BFBC2: 1920x1200 everything maxed, 8AA, 16AF, novsync/hbao, 60-70fps average, i've seen it drop to 30fps when a UAV air strike hit my face and i didnt die