Personally, I don't like running a GPU over 80C. Someone implied that their (one year old card?) card hasn't died yet running hotter, but that is definitely no proof at all it won't die prematurely...
Trust me, they are designed for it, check the whitepages on ATi or NVidia.
Ive been running a 9800GTX for almost 30 months with temps reaching 85 Celsius regurlarly and it hasnt had a hickup yet.
Must add thats its a pre oc-ed one and I never got it higher, tried, but didnt work.
So to say it will die prematurely, is a bit shortsighted in my opion.
Read the net and reviews and youll see it common nowadayds that gpu's run that hot, since gpu computing and gaming are getting more and more gpu intensive.
Ill bet there are even people out there, that fold or grid on it and they run systems 24/7 for years and years with the same cards and having zero issues and they run temps around the 80's/85's too, just like on my system, especially if you have 2 or more cards on the same board.
You really think that gpu manufacturers havent thought about it?
As long as you dont fiddle with voltage tweaks, get a good case airflow and keep it under 90C youll be just fine.
But thats mine opinion