Well if your frames are unlocked then a higher GPU usage is to be expected as well as higher temps. But anything close to or above 80 is pretty toasty.
Your GPU won't die on you but anything close to 80 is cutting it close and it won't help its lifespan in the long run.
A clean heatsink/fan is a factor, but only if paired with proper airflow. Doesn't matter if the fans are working unobstructed when they're blowing hot air on the GPU. So make sure that you have a good airflow going on, and that can be achieved by managing your cables and adding intake/exhaust fans.
But all in all your GPU will throttle itself before reaching dangerous temps, but running too hot for too long can and will reduce its lifespan so make sure you take good...