Tried again, this time with a clean driver install, but no luck...

Everything seems to go smoothly for a while, but then it gets stuck, and all I can do is to reboot my PC to get the "normal" clocks again.

Also the problem seems to start as soon as I try to change the memory clocks.
If I move them to anything other than 2000 MHz (in Afterburner), it gets stuck.

No matter the load on the card (with Kombustor running and GPU ussage at 99%), they all remain on those values (800/1600/325 => core/shaders/memory).