A point I want to raise. If you need to max out the fan speed on the gfx card for it to run stable. Something is wrong. You probably have a airflow problem in your case. either your intake filter are dirty (if your case have them), you don't have enough case fan (or they are at too low a speed) or you have a air circulation problem (your air circulation pattern is leaving a pocket of warm air near the GPU).
OR that the gfx card has/had a problem
I had two 8800GTS512 & all was fine but for a little problem both had the fan maximum blocked at 50% (even though that's not what the default BIOS said) which caused problems with memory temps with some rare games ...
of course it could be solved with manually forcing higher fan speeds with rivatuner.(generally 60~70% was enough)
This was just an example to show that not everything is black & white, while you got a point, the universe of possibilities is wider than that.