And I use the Debian package sysfsutils.
In /etc/sysfs.conf I have
Specs: Sapphire Vapor-X Radeon HD 5770 1GiB with git r600g on Debian Wheezy [testing]. I have a button in my Xfce Panel to toggle between Low and High. After a little gaming, switching down to Low yields a noticeable difference in fan noise, and the GPU temperature drops to 39 C or so (today it's down to 34 C).
module/pcie_aspm/parameters/policy = powersave
class/drm/card0/device/power_method = profile
class/drm/card0/device/power_profile = low
owner class/drm/card0/device/power_method = root:video
owner class/drm/card0/device/power_profile = root:video
mode class/drm/card0/device/power_method = 0660
mode class/drm/card0/device/power_profile = 0660