I have a stock diamond 7970. I ran FurMark. Temps maxed at 80c.
I started messing with CCC. Everything was at normal settings. I read here on tomshardware to start with the clock before memory. So I maxed the GPU at 1125. Ran Furmark again in "Dynamic camera and Post FX"
I was only getting like 25fps then when the fur ring was on a close up the computer crashed. I started normally... then did a clean reboot. Dropped my clock speed to 1000. Ran it again(furmark)... Crashed..
I then tried borderlands 2 just to see if furmark was screwed up.. borderlands started producing tons of artifacts.... then crashed...
Just now, I set the cards clocking speeds to default from CCC.. Ran Furmark fine.. but borderlands crashed after like 5 mins.
From what ive read these cards should take max settings within the CCC without messing with the voltage with no problems.
I havnt tried afterburner yet because I read that you should start with CCC first then once the card checks out... then move to advanced OCing.
With the core speed at stock, and it still crashing on BL2, I think that may be a driver issue. I have a buddy with a 7950 that's been having tons of problems with artifacts and screen tearing on BL2 (only that game). So you could possibly Google that up and see if any others are having that problem, or you can update to AMD's newest drivers.
As for crashing on FurMark, some cards overclock better than others... A lot of the cards are good for just sliding the bars on max 1125/1575 with stock voltage and have no problems. However, some are just crap. My stock 7970 isn't too bad since I can run 1100/1500 all day long with no problems, but once I put the core or memory up any higher, I start to get artifacts within 3-4 hours of gaming.