You don't need to worry about the fan, its rated for years of abuse at 100% fan speed, I would just make sure its not full of dust.
How is your case airflow? the reason I ask is because 85% fan speed is quite high to maintain a temp of 85C.
Its weird because my case airflow is fine,
*all the fans are 2000RPM
2x side panel intakes
2x front panel intakes
2x buttom intakes
3x top exhausts
2x rear exhausts (CPU cooler push/pull)
With all that airflow the card still gets really hot. Dont really know what else i can do to keep it cool, already filled the case with fans, most of em blowing cold air into the case. I think part of the reason its runs hot is because its ontop another video card just sucking all that heat, also it has a stock cooler with just one fan. But yeah inside the case its cool but its not enough to stop that card from heating up crazy, its an EVGA GTX580 SC btw.