Well, you can look at it like percentages. Onto the larger part of this quote: the OC. My core clock speed is 950Mhz, I am thinking about overclocking it to 1000Mhz just to get through that 'magical barrier' how much of a performance/heat increase would that mean? (And i still don't really get if it's good or bad to run the fans at 100%, im confused xD)100% fan speed kills fans quicker, simple as that. When i run BF3 on auto-fan settings the highest i have seen so far is 68 degrees Celsius. Idk why Djinni said to run them at 100%, doesn't seem like him. With an aftermarket cooling solution like the MSI TF II/III (Hawk is a designation for the OC on the card), Asus DCII, or Gigabyte's triple fan, you should never need to have the fans at 100%, it is a waste of the extra energy being used to power them, killing the fans sooner than prolonging their lives, and causing far more noise than most people would prefer to hear - and ultimately the reward of a few degrees lower from an already safe-zone anyways is just not worth it. If the monitors are off, like when I'm sleeping/away from my computer, the GPU drops all the way down to about 20-23 Celsius.

Right now I'm not gaming but due to dual-monitors forcing my GPU to have the core speed at the high setting (880MHz in my case, I saw no reason for the OC anymore since SW:TOR is a cake walk for the 560 Ti at 1080p) the fan is at 40% and my GPU is at a cool 37 Celsius. So if the GPU is at 60 Celsius, the fans go at 60% and keep it perfectly stable. I have my MSI Afterburner set to make the fans be at 40% (they won't go lower) till it hits 41 Celsius, which is where it starts going up 1% speed per degree Celsius. They WILL get loud at 100% speed and just because you're gaming doesn't mean you need to have the fans running at 100%, as games like WoW, SW:TOR, and many others don't even work the GPU that hard and thus won't even put it anywhere near dangerous temperatures.

Running a 560 Ti MSI TFII/III fan at 50% all of the time or just letting it do its own thing, is personally, the optimal choice.

Msi afterburner fan