If your car is one of those FSS cars, then you should be using full synthetic. Regardless of which oil you use, it should be nothing less than xxW-40.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section