my Sapphire, I forgot Sapphire good brand, hd 7950 is 5 years old and still running.
the main issue with GPU's is cooling fan failure, hence my suggestion for a dual/triple. some cards are now equipped with easily replaceable fans.
if you keep it clean and cool there is no reason why it should not last many years.
a low quality power supply can shorten the life of components. keep in mind.