How exactly does lower heat = better performance other than the scenario that you are overclocking the bageeebus out of it up to the thermal limits?
If that is the case then realize if your fan fails your card will crash and burn faster than a McCain jet. If you are taking the stock fans to such a limit, a 3rd party cooler with a 120mm fan may better suit your needs...or even water cooling if you are so inclined.
Anyway...IMO I wouldn't rely too much on my crappy stock fan if I was running it at 100% 100% of the time. But, keep it at that and then post back so we all know how long they last