(In reply to comment #1)
> Please attach the Xorg.0.log and the output of dmesg and glxinfo.

Will post those later, when I'm back at that system.

> Is this with DPM successfully changing clocks?

As written in bug 74250, comment #8 reclocking doesn't seem to work for me.
Whatever I've been doing, the output of cat
/sys/kernel/debug/dri/0/radeon_pm_info /sys/kernel/debug/dri/64/radeon_pm_info
stays:
> power level avg    sclk: 30000 mclk: 15000
> power level avg    sclk: 30000 mclk: 15000

(observed through a SSH connection, in order to keep the 3D applications
running fullscreen). I can check the clocks with e.g. MediathekView too, but it
would be very weird if the GPU would reclock for "simple" applications and not
for the 3D applications, wouldn't it?