GPU Overclocking--Core Stable, Memory Stable, Core+Memory=Unstable

[earwicker7]

I'm overclocking my Crossfire-enabled XFX Black Edition 5970s with MSI Afterburner, and have run into a bit of a wall.

Using a core voltage of 1.174V, I was able to get the core stable by itself (using GPUTool for stress tests) at 900MHz, and the memory stable by itself at 1200MHz; by stable, I mean ten minutes of GPUTool with no artifacts/crashes. However, if I run the stress test with both overclocks enabled, I get artifacts fairly soon. The maximum temperature on any of these tests has been 86C.

So I'm guessing I need to lower either the core or the memory speed; my personal belief is that I should lower the memory first, as the limiting factor in the tests so far seems to be the core speed... the reason I'm saying this is that, when I test the overclocks on their own, the average FPS with the core is 61, while it is 65 with the memory. Does this sound correct?

One last thing... the highest GPUTool has been able to get the GPU usage is 92%. I'm guessing I would want to have it at 100% to set the overclocks... is there a program that will make it hit 100%?

 

[Sean W.]

use FurMark <- click


drop the memory, not the core.

 

[earwicker7]

FurMark stresses them to 99%, but it will only run one of the cards, even with the multiple-GPU version

 

[Sean W.]

do you have crossfire setup?

 

[earwicker7]

According to GPU-Z, and Afterburner when I run GPUTool or a video game, yes. I'm not using the Catylyst Control Center, just the drivers... maybe that's freaking it out. Weird.