I lived in Alaska for 15 years and discovered the real value of
synthetic oils. After losing 2 rod bearings in 2 rebuilds on my Chev Blazer, it was using premium Dino
oil, I switched to synthetics and never looked back. My cars always started easily in the cold weather and had excellent
oil pressure in the summers (yes, it does get warm in the summer up there).
I always used premium quality
oil filters as well. Those included
Amsoil, Mobil1, Wix, and the high-end Motorcrafts. Change interval for synthetics is much longer than the 3000 mile recommendation, and the Hondas I owned recommended 7,500 mile intervals.
When I moved to the lower 48, I started racing motorcycles and got a real education on oils from a race bike engine builder in Bremerton, WA. He recommended zero weight
synthetic race oil for my highly tuned single cylinder race bike. I used it and it worked great. I got measurable horsepower over the Dino oil I was using. Never seized, never lost a bearing. Don't think you could come close to that performance with petroleum oils. Bear in mind that I never broke in a motor successfully with
synthetic oil. I always used Valvoline racing oil for breaking in rings and cylinders, then switched to synthetic. I used Torco, Mobil1,
Amsoil, and Redline for racing.
As for the 60's engine I have in my Cobra.......... I broke it in with Valvoline 10w30 and then put
Amsoil synthetic in and........... no leaks, starts quietly, runs strong and I don't sweat the oil change interval. I only get about 5K to 8K miles a year on my car and change the oil and filter before putting it away for the winter.
Just because they were built before synthetics were around, doesn't mean that synthetics don't work on them. Any engine, air or water cooled, can perform better on synthetic oils. Premium oil filters are a must with the long change intervals for synthetics. Depending on driving conditions and the kind of air filter you use, you need to change the oil filter accordingly. Cheap insurance, even if the good ones cost $12 - $15. If your oil filter costs less than $10, it isn't premium and 3,000 miles would be max.
My totally humble opinion. I'm sure others will weigh-in with their's as well.
Paul