Do you really need 100% cooling?
I wouldn't suggest this but It's really a necessity than turn it on! Remember, the video card is more precious than a cheap fan. I do perfer a fan speed around 90% or 96%.
If it runs above 60C, yeah, It should be 100%.
What i would do is Download AtiTool (most stable version) and configure the fan speeds under the chart. There is a little chart where you can put how much fan speed along with the temperature. Example: 40C = 80% fan speed. I use this personally it's wonderful. You don't even have to run ati tool for this because it saves it automatically. Also, if you want defaults back, there is a default button that clears and resets the settings originally.
And Remember, the Video card is more precious! Cooling is very important!
I hope this Helps Good luck.