These modern formulations all have enough
Here is one data point
Last weekend I was racing with some pals. The car’s are all 1974 and older, and all run vintage motors (no modern LS or coyote crate motors). Our pistons and valves are modern and some run steel cranks and modern forged race rods. One of the guys, Bob, blew a head gasket at the end of the first day. He is the sort of guy who then says, “I’ll install a new one after dinner.” He is 10x above me in knowledge and experience.
Since there was plenty of time we kicked back and talked about oil. I asked him about his experience using Mobil 1 (15w50) in his nearly 50 year old European twin cam motor.
It was his experience that even the old style motors do better on modern type oils (with enough ZDDP) due to the advantages of the vastly better temperature and wear stability and their higher wear protection. He also said yes they can leak a bit more on old motors because they don’t start to thicker and sludge up fast like conventional oils. We all run modern seals where possible and catch cams on our race cars to keep the track clean.
Anyway, if I could get a full synthetic 20w50 with zddp for $3/qt, I’d be using it over conventional oil. I might not be right. It’s just another opinion.