MB recommendation: 20W50, 15W40, 10W40, 5W40, 0W40, 5W30, 10W30, you can use either of these oil in that order of preference, for your climate. I would suggest 5W30.
Low temperature is the variable. Engine operating temperature is the roughly the same winter or summer, whether the ambient temperature is -10 or 100F.
To minimize wear at start up, something like 5W30 works pretty good. Once the engine is at operating temperature, it does not make any difference if you have 5W30 or 20W50.
5W30 flows much better. MB recommends it for all ambient temperatures. So do other manufacturers. Oils like 20W50 are only recommended for certain temperature ranges. Select oil viscocity according to the lowest air temperature expected before the next oil change using the latest MB chart, is the MB recomendation.
I went from 10W30 to 15W40 and I have noticed that it takes longer to build up oil pressure. At idle, the pressure stays higher. I am going to 5W30 conventional or 0W40 Synthetic on the next oil change.
94 E320 58000 Miles