Simply look at your owner's manual for which weight oil is to be used for expected temps. My nieghbor has a '91 Audi 100 and it calls for 15W-40 or 15W-50. I don't think there is an oil sold that has a rating less than SJ, including Delo 15W-40. One of the things I have noticed written on the back of heavy weight oils, is the words "provides superior protection". I don't find this on lesser weight oils like 10W-30 or 5W-30. Just a little interesting fact, one of those "Hmmmmmmmm" things.
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