I'll have to weigh in with JackD and Jeff. I work with a respected consultant who's an expert on oil/tribology. He's an STLE member and conducts 4-ball and wear tests on different oils and additives. He not only lets me know what's what, but he shows me data to back up his thoughts.
Automotive engines don't need heavy weight oils. Even 30W isn't necessary to prevent engine wear. The only reason lower weight oils aren't commonly used is that oil loss due to evaporation at operating temperatures becomes a factor. It's hard to make these low weight oils. These new lower weight oils such as 5W20 can ONLY be formulated using synthetic stock to preclude oil evaporation. They're not bad oils - just expensive.
Like I've said before, there's too many opinions about oil. It's like listening to Frasier and Niles Crane discuss the nuances of motor oil! Just change the engine oil and filter every 3000 miles or so with commercially available SJ oil and your engine will live a long and happy life.
95 E320 Cabriolet, 131K