>Are there any issues with the extra zinc damaging the >cat after thousands of miles you are aware of?

Norcal--I can't see that there would be any more issues with it than with someone using motorcycle specific oil, because that oil also has additional zinc additives for smooth tranny shifting. Additionally, unless the engine is burning oil, I can't see that zinc in motor oil would affect the cat in any event. Further, even if it did affect the cat in some way, the worst that would happen is that it might affect the ability of the cat to clean up the exhaust, but it certainly wouldn't clog the cat or cause any performance problems. I've never heard of any kind of cat problems on bikes from this type of thing.
I'm not an engineer so these are just my opinions.
Lee in the Mountains of Northern California 8)