My 290x gets that hot quite often, never a problem and I believe they'll crash/throttle before anything serious happens.
Question for you. What are you using to control the fanspeed and are you sure it's running full speed at that temp. I'll bet is really loud when running at 100%.
It's normal, the default temperature target for this GPU is 94c. If you increase the fan speed to 100% and set the target temperature to your liking, the GPU will use the least amount of fa speed possible to maintain that target temperature. It's perfectly safe to run the GPU at 94c or lower.