What's the best oils for tappet cam engines?

Talk to any of the cam companies. The most critical time for zinc content is during breakin. After that, broke in is broke in. Low zinc motor will not cause camshaft failure after it has been properly broken in with a high content zinc oil. It's not necessary after breakin, although plenty of people do it. While I think it's good insurance, it's not necessary after breakin. That's straight from every major camshaft company I've talked to about it.