Whenever I start mining with guiminer and then start up GPU-z, my computer will instantly freeze and require a hard reboot. Conversely, if I start up GPU-z first and then click "start mining" on guiminer, it will do the same.
More importantly, I have the same issue with the Catalyst Control Center. But, it's even worse: If I make some modification from the default (such as set a manual fan speed), then close the program, and then start mining, it will crash.
Because of this, I cannot adjust fan speed while (or before) mining, and I will probably not be able to OC my cards. This also means I cannot monitor temps while mining. I've been able to do a bunch of other things during mining though, including web browsing. Also, I've been able to mine for a couple hours now without touching GPU-z or CCC.
I have not tried a third-party program like MSI afterburner yet.
I'm running 2 6970's (crossfire enabled) with a 1000W psu.