What causes a GPU to get lower minimum FPS while overclocked?

[toneekay]

This is a general question for those gurus out there... Over the past couple of day I've been overclocking my video card (MSI GTX 560 Ti). I'm able to push the card to high limits, however, everytime I run a benchmark test on Unigine Heaven for example, I notice my minimum FPS gets lower (this is a bad thing).

I don't have the exact numbers of each of my tests right now (since I'm at work), but it's gotten me curious... So far I've done three tests: Stock, mild OC, and high OC. My average, minimum, maximum FPS, and overall score seems to be higher from stock to mild OC, however, from mild OC to high OC, the minimum DROPS lower as everything else bumps up higher. What can be the cause of this?

Off the top of my head, these are my clocks:

Stock: 880/1760/2100
Mild OC: 970/1940/2300
High OC: 1000/2000/2450

 

[mjello]

instability

 

[thesnappyfingers]

could be that your PSU is unable to adequately supply the needed power under those load conditions.

 

[toneekay]

instability

In the back of my mind, I was thinking this as well... however, after testing on Kompbuster and running a few benchmarks, I've recieved no driver crashes, artifacts, or any other signs showing instability.

could be that your PSU is unable to adequately supply the needed power under those load conditions.

I have a high quality 850w psu... I'll be damned if it wasn't supplying enough power.

 

[toneekay]

Could it be possible that my memory clock is higher than it needs to be, and the core/shader clock isn't working fast enough to keep up? (I guess this would be a sign of instability)