Sorry, I was wrong after all. After 2 days i got a lockup again and went back
to the old method.

When i don't set DPM at boot GPU is overheating and the fan goes crazy. When
setting performance to something other than "high" - lockups happen.

I'm on Ubuntu 14.04 and using kernels from
http://kernel.ubuntu.com/~kernel-ppa/mainline/