Anyone have any opinions regarding OCCT as stability benching?

I recently got my GTX480 under water, and done some benches using Kombustor, Furmark, Vantage, Dirt2, Unigine and OCCT.
Seems like whenever I go above 875 / 2001 on either core/mem - every test except OCCT kinda gives a "true-false" result. Especially Kombustor and Furmark doesn't show any artifacts or instability above like 900/2200, although both Vantage and Unigine show instability and OCCT gives loads of errors

Anything above 850/2001, I've set voltage to 1.2 in AB.