The Factory Approved Service Product booklet shows 5W30 is okay for ambient temperatures above 86° for my car.
A lubication consultant I work with says engines normally don't need anything above 30-weight. He says even lower weights would be acceptable if they could be made cheaply. The problem with dino oils lower than 30-weight is that they would volatilize in the engine.
I normally use 10W30 because I prefer oils with less range. Wider range in an oil means it has more additives. It is these additives that quickly degrade before the base stock does during the life of the oil in your engine. I used 5W30 this time because I wanted the lower viscosity to hopefully help flush the contaminant that caused the ticking.
95 E320 Cabriolet, 131K