I'm deciding on a long-term oil to use in my 1955 Jaguar XK140 engine, now that it's done 1500 miles since rebuild on Castrol 20W 50 classic oil. Main bearings are at around 0.001-0.0015" clearance, big ends at 0.0015-0.002".
I have an old Mustang which has always run on Fuchs Titan Pro R 15W...