Best rocker arms ?

I have always wondered about the longevity of aluminum rocker arms. I saw a letter recently (don't remember where) where a person in charge of maintenance on a fleet of trucks asked about using aluminum rocker arms with a higher than stock ratio. I think he was asking if the extra power & possible mileage increases would pay for the rocker arms. If I remember right, the answer he was given was that the aluminum rocker arms were only good for about 20,000 miles. That might be fine for a race or limited use street engine, but I would think it's just a problem waiting to happen for a daily driver. I plan to stick with steel rocker arms.