Great. If you're using use_gmux=1, you most probably unloaded and reloaded the driver with the new option. Then, gnome-power-manager still uses its previous settings. In order to get more appropriate settings, you also have to kill and restart gnome-power-manager. What happens then? Does the backlight change? Does gnome-power-manager employ a reasonable step size?
Great. If you're using use_gmux=1, you most probably unloaded and reloaded the driver with the new option. Then, gnome-power-manager still uses its previous settings. In order to get more appropriate settings, you also have to kill and restart gnome-power- manager. What happens then? Does the backlight change? Does gnome-power-manager employ a reasonable step size?