https://bugs.freedesktop.org/show_bug.cgi?id=110865
--- Comment #24 from Martin mwolf@adiumentum.com --- I am so sorry to hear that Dieter, this is really terrible. But I can assure you your English is fine.
I also think your problem is somewhere else. You mentioned it yourself. and I think Alex Deucher did as well, that your P-States are not changing.
I have two different screens. One HP ZR2440W connected via DVI and a Dell U2412M connected via Displayport. Both run at 59.95Hz@1920x1200