Nope, I haven't, but that's something that I've thought about. I have a friend who put a set of Erson rockers on his engine and lost a bunch of ET over the standard rockers. Doesn't make sense to me, but its something I wouldn't mind investigating. I'd figure that any power losses or gains would be the result of variation in ratio, rather than in reduced friction from, say a roller tip, or something like that...
