I am new to overclocking, and I am looking for some quick advice to overclock my HD 6870 Vapor X edition. I am currently using Sapphire TRIXX software and my questions is: How do I know if I have a stable overclock? Aside from the obvious crashes, is there a stress testing program I can run, and is there a specific fan speed/temperature that would make the OC stable?
Core clock is at 900
Memory clock is at 1050
The newer ATI/AMD cards are a bit different than the old ones. They have "error correction" built into them, so you probably won't see artifacts like the old days. What happens when not stable is the card will appear to be losing performance as resources go to correcting the errors. That doesn't mean you won't crash, it just means you might not see anything irregular.
Your best bet is to keep an eye on FPS and make sure your not going backwards as you push you overclock forward. Obviously a frozen screen or a complete crash will tell you something.
With temperatures the general rule of thumb is to keep them under 80c if all possible. The fan speed doesn't matter as long as temps are good and the noise isn't bothering you.
The 5 series does too, my 5870 depending on the settings was slower with a higher overclock. I didn't see anything in games but occasional lag but the benchmarks were a decent amount less. For example at 980 on the core I was getting a lower 3dmark11 score than with 950mhz.
Just test with fraps before and after, then compare and contrast, you should see a difference. I use 3dmark11 to basically see if my setting are making the difference I want. If I don't crash or freeze during 11 and the numbers are better than before, I'll basically game for a while and see how it goes. I personally don't stress test the gpu anymore, unless you consider 3dmark11 or gaming stress testing.