I can also confirm power management is very good for me on 5750 and 5770 cards. In idle states GPU are about 10C colder than they were by default, thanks to lowest frequency possible. Then they quickly increase frequency on load, so there was no noticeable performance loss either. Really remarkable improvement!
And btw, I can monitor GPU frequencies like this:
And file contains something like this for 57xx GPUs:
while (true) do cat /sys/kernel/debug/dri/0/radeon_pm_info; sleep 1; done
So I guess its possible to monitor GPU frequency in tests as well. Though it changes quite often.
uvd vclk: 0 dclk: 0
power level 0 sclk: 15700 mclk: 30000 vddc: 1000 vddci: 1000