Although some cards can take up to 100c I would personally recommend to keep it under 85c. I would try increasing the fan to a higher rpm like 75-80% and see where the temp stays at those speeds. Then try to lower it in increments of 2.5% untill you find a happy medium where the noise is acceptable to to maintaince it below 85c. You might even consider a utility to automatically adjust the fan speed according to the temperature of the GPU.
If you are not overclocking you should not have to mess with the fan speed at all. Every card runs different temps. 85C at load is find for a GPU. Are you experiencing any issue? If not, just leave it, you will be fine.