Hi Lyle;
Much appreciate the feed back. And, I agree that on a vehicle used daily the thicker 20W50 oils are better. But, if you don't drive your vehicle but twice a month or less, then thinner viscosity oil is preferred, even with our tolerances. If you read the factory oil requirements they are in the 10W30 range and for a reason.
Cooler climates require a thinner oil to lubricate the engine components during cooler weather.
Our vehicles (you in Florida and me in San Diego) run in a warmer weather condition so the thinner oils are not needed.
But after setting for several weeks leak down of lubricating fluids leaves our engines in an almost dry start up mode.
Which can cause more damage.
Even present day oil requirements state that if your trips are short and mostly in town then oil changes should be more frequent.
So, depending on the use of your Honda 600 there is and should be different oil viscosity requirements.
And as ZDDP mainly relates to over head valve/cam trains using tappets there are some good qualities associated with ZDDP (see the following URL)
http://classiccars.about.com/od/mainten ... ditive.htm
But as the article states to much can cause more wear, and the Honda 600 engine has no tappets, rather the same qualities of a roller cam unless your rockers are out of adjustment.
Just my cut…
Bill