The weight that is used in oils is heavily dependent on your local temperature and engine in the vehicle. If you are in a very cold environment or if your car is parked outside, you want a oil that is very flowwable at low temperatures. So you pour in 0W. But, then the higher rating depends on the engine itself. If the engine is high mielage, high stress, and runs hot you may want a 40 or 50 weight. Also, if the engine is a iron block then you might want a heavier oil and if the engine is an Al block then you can use less viscosity because Al dissipates heat more. FSS cars require 0W-40 but according to my service advisor, Mobil 1 10W30 in So Cal can be used in these FSS cars but not for extended drain.

So as a fellow 300E brethren, I'll give you my advice. The 300E likes its 20W50 and 15W50. So, to syn or not to syn, is basically a cost factor. If you are burning oil then you don't want to be burning $5 a quart oil so I would use a dino oil such as Castrol 20W50 or Chevron 20W50. But, because you live in the east coast, you definitely need a 0w or 10w. The 20W does not like flowing in the cold and won't protect your engine as well in the cold. If you want to syn, living in the east coast, use Mobil 1's 0w-40 Euro Formula.

Alright, no more oil discussions. Maybe MercedesShop can make an encyclopedia on motor oil and sell it to the public as the definitive guide.