I'm not near the expert Willys36 is, but I do know that aluminum fatigues/cracks/fails much more rapidly than steel. And that's why I went with the steel roller tipped ones.
BTW, has anyone here actually done a weight comparison between the two? I mean, besides the friction differences between the bearing pivot and ball pivot, Is there that much to be gained inertial mass wise? When you visually compare the two, the aluminum is massive in comparison to the steel rockers.