Overclock Sapphire 4870 dual slot

[Informant]

Hello.
I recently acquired a 4870 from sapphire, dual slot version.
I try to Overclock , but I have not found on any test zero frequencies suitable for this type of card.
The auto tune CAC gave me a frequency of 840, which I quite enormous, given the base frequency.
Could someone give me an Overclock stable and safe for the card?
Thank you and good evening

[Aikonik]

"The overclocking is not an exact science"

We need you doctest, many factors influence your final overclockign in / brand / quality / design / power / temperature ..

[Informant]

So good (I think), I turn on a corsair 650W power supply, and the temperature is 60 to 40 degrees

I launch a 3dmark vantage by one hour, the time to finish my job .

[Dr. V]

Could you tell me about the used softwares? I edited every clock with RBE but GPZ-U still show 750Hmz and my 3dMark score proof is. (Sapphire 4870) Should I uninstall CCC?