okay awesome, I can't remember where but I thought I remembered reading that the strain from it running at 100% constantly could lead to the cards life being shortened.
That might have been referring to the fans. Obviously they are mechanical and do suffer from wear and tear.
Just a little FYI. I've been running a pair of 970's at 100% load with a 100mhz overclock, 24/7 for the past 9 months. They're actually running the Folding@home program which requires much higher levels of stability than mining or gaming does. Therefore undervolting is out of the question, and sometimes overvolting is needed to keep an overclock stable. Side effect of this is higher power usage and more heat. I've had the fans set to run 100% since day one, and just recently I've noticed a little "whining" starting, and also a little oscilation in the fans rotation.
For the AMD cards, using 280x as example, the default core voltage is 1.2v, but it is too high, usually, 1.12 could support the 1000MHz core frequency.