I still prefer the synthetic 5W-40 HDEOs because they have the additive pack, operational temperature range for air cooled engines, shear stability, and leeway for inevitable shear without compromising cold weather performance or being so thick as to impede cooling on the hottest days. The HDEOs are also meant to handle lots of soot and contamination, far more than PCMO.
IMO, the OP should do his homework looking at used oil analysis from older diesel engines and compare these used oil analysis to HTHS and other metrics of the oils in question. VOAs are nice to see, but they tell you very little about how fit for use an oil is. While we know that zinc and other additives are one good ways to provide the protection needed, I think the OP would do himself a disservice to make the decision based on their presence in a VOA. There are many additives that can accomplish the feat of providing this protection and the only real test of their ability is to look at used oil analysis from engines that are known to be hard on oil or have flat tappet cams.
That being said, I chose RTS for mine and would recommend the same without hesitation.
I use it in my 1984 8hp 3600RPM Briggs mounted on a Coleman generator. It's been through a few hurricanes and some other stuff, too. Still runs like new. It's only ever run RTS and Mobil 1 10w30 (Previous owner).
