Phillips also make a 20W 50 which I use in winter in an O360.
Bottom line --- how and why you warm up an engine is very dependent on the type and condition of the oil. No way would I use much more than idle rpm until the numbers are "in the green", and where relevant, the oil cooler thermostat is flowing oil through the cooler.
I don't necessarily disagree with you but what damage/wear is going to be caused by running the engine up above idle before the oil is hot? I don't mean take off power, but say 1500 to speed the warmup? And is a radial any different than a flat engine, supercharger aside.