When gaming 85C is not that alarming, these cards can handle temps of 95C or above while gaming and will last for years.
Applying thermal paste is a good idea, but its not as easy as applying to CPU, especially if its your first time doing it. So be careful or you could damage the GPU. See some videos on YouTube and read some forums before you try anything. And you will need proper tools to disassemble the GPU. Good luck.