ATI Radeon 4330M (X.org driver) overheats since upgrading to Xubuntu 12.10

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http://askubuntu.com – since upgrading to Xubuntu 12.10 the ATI Mobility Radeon HD 4330 chip in my Laptop (Acer 4810TG) overheats after about 5-15 minutes (depending on start-up temperature) of light use and shuts down the computer. This doesn't happen under Windows 7 and has never happened under Linux before the upgrade. The card runs in dual-head mode using the HDMI output. I've already tried using the card in the low-power profile (/sys/class/drm/card0/device/power_method contains profile, I wrote low to /sys/class/drm/card0/device/power_profile while the system was running (and checked that it was actually wri (HowTos)