If you use furmark you will need to rename the benchmark file form Furmark.exe to anythng you like ATI "fixed" the drivers so that it throttles 48** cards during the benchmark to stop people bricking their cards.
Anyway the Catalyst control centre auto overclock thing does not really test the overclock very efficiently I will be quite surprised if when playing games it didn't artefact after a while.
Like Watercooled suggests use FUrmark to test temps (it will get hot) and then ATItool or ati tray tools to check for artefacts.
Furmark -
http://www.ozone3d.net/benchmarks/fur/
ATI Tray Tools -
http://forums.guru3d.com/showthread.php?t=275077
ATI Tool -
http://www.techpowerup.com/atitool/