T5 bulb replacement time

I've decided to switch fully over to T5s on the 55. Just bought the ATI dimmable Sunpower fixture. My question is on bulb replacement time. Does a quality fixture extend bulb life? I've read of some people using this fixture using bulbs for 18 months. ATI claims "Superior design and high-end components produce 50% more light than most other equally-sized T5 fixtures. An active cooling system allows bulbs to run at a more optimal temperature, improving both bulb output and bulb life." But how much more life?