My whole life i was told that most engine wear happens when i start a engine, especially when cold start.
That 10w- Oils need much more time to reach all parts, to build up pressure, to lube all parts, especially the parts far away from the pump. Camshafts etc.
The engine runs for some seconds without proper lubrication, causing wear. The cold start clatter means wear, in my opinion.
When i start my car after it sit for one or two weeks, the oil pressure light sometimes need one or even two seconds to go off. To me, this means unnecessary wear of the engine.
When i start the hot engine, e.g. after a fuel stop, the oil ist thin. The oil pressure light go off in the blink of a eye. No engine wear.
I am very affraid of cold start wear and will continue to use 5w- or 0w- oils even in Summer.