I have tried to overclock my card. Seemingly it worked, and the GPU-z shows the OC speed (see GPU3.png). However, current readings are REALLY far from the normal speed of the GPU. That's what I can't figure out. I mean... it runs way too slow compared to the results I have found.
Pictures: (click to zoom in)
Counter-Strike Source with fps_max turned off
Furmark's burn-in test
GPU-Z showing the OC values
Due to Brian's comment, 91% of fan speed. No effect. Still underclocked.
I have a fairly decent (I think) PSU. A Corsair Enthusiast Series 750W v2.
The GPU is: Zotac AMP2 GTX 260^2
The power pins are also connected. Any idea? :-/
I've checked "GPU-Shark". It says, my GPU is in the State 3. I'd need State 0. The highest performance.
Guess I'm on the right track! There is an application (God, or whoever ... bless the author), which lets you choose the power state by hand. Thus I have the normal speeds after setting it to Power. (WARNING: Select APPLY & Reboot. My OpenGL drivers crashed right after I used "Apply Instantly".) Anyway, so far so good! If this works, I'll post it as an answer.