It seems that zinc is only important during camshaft break-in on a flat tappet engine. Once that original wear pattern is established, the zinc concentration becomes much less important. The retailers of "high zinc content" oil have found a good way to pick the pockets of gullible people, I think! It's sort of like the folks who tout other "mouse milk" oil additives like STP, etc. I attended a seminar several years ago hosted by a research chemist for Kendall Oil Co. and the question was asked about "additives". His answer went something like this: "We use 22 additives already- - - -17 of them are beneficial to your engine, and the other five offset the bad effects of those 17! That's good enough for me!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!