GPU stress test?
 

For the last few days I have been trying to achieve my old GPU Overclock and have been running into some problems?
I had a nice 720Mhz on my GPU Core for a OC, Now I can't get past 700Mhz?!
But here lies the issue. I just found this tool called GPUTool from techpowerups website. So I ran it and put my Core clock up to 702Mhz. I ran the GPUTool stability test for 10 mins with no issues. Temps were around 80-81C once my GPU warmed up.
But before I decided to go any higher I tried to use ATITool again to run its' Artifact scanner on my 702 Core Overclock. BAM!! Major Artifacs right off the bat So I shut down the Artifact scanner.
Next up was MSI Kombustor, I ran it in the openGL 3.2 mode, Stress tested it for ten mins also. No errors or Artifacts!! Temps got a little warm, Hovering in the 88-89'sC for most of the test once it was warmed up.
Which program should I be trusting for stressing my GPU accurately? One app says its a good OC, The other says it's way off?
I could also try the Real Furmark App too, Along with the new GPU test in OCCT 3.0?
I just want your guys input on what you think is the most reliable GPU stress tester?
I know that gaming is also a very good indicator too. But my worry is that my GPU will be Artifacting and I won't be able to see it which will cause major damage.
So, basically, What your favorite GPU stress tester and why?
My hats off to the Best Overclocking Website going. I always trust this site over anywhere else

ATITools is discontinued and I have no idea if it's accurate on newer video cards.
If you want to heat-up your GPU use Furmark/OCCT/Kombustor but usually playing games is a real-life test.

I Ran stalker COP with my core at 702Mhz for over 45 Mins without a artifact that I could see! And ATITool showed Artifacts at that same speed?? I think I will stop using ATITool. I did run Kombustor, GPUTools and Furmark all for ten mins at that speed and none of them showed a artifact. Gone is ATITool. Wonder why EVGA doen't have their own stress test?
Thanx and cheers:)

atitool and other benchmarks give you a worst case scenario - artifacts that show up in benchmarking/stress testing tools might not necessarily show up in games.

atitool could be stressing a part of the card more so then the other stress tools.