I've also used 20w-50 in every engine in every car I've owned since about 1973 or 74ish, except for my 2006 Mustang which the factory says to use 5w-30 in, and never had any problems from using it. Brands used were Castrol, Valvoline, Chevron, and Wal-Mart's house brand. Engine clearances were all standard.
When I was in college a whole bunch of years ago, I went on a tour of the Mobil oil refinery in Carson, CA, and found out some really interesting things about oil. The most interesting fact was that in a given geographic location, all commercially sold oil come from the same refinery. For example, ALL the oil in the south coast/ Long Beach area of southern Califoria is Mobil oil, regardless of what the label on the can/bottle says. Mobil refines the oil and then sells it to Exxon, Shell, Castrol, etc.,etc., who then package it in their own containers for retail. The only difference between brands is in the additives, and even those are almost identical. The most important thing to look for on the oil bottle is the SD/CC rating and the viscosity (10w-30, 20w-50, etc.) The brand name is relatively unimportant. Wal-Mart buys their oil from the same place that Chevron does. Pretty much the same thing with gasoline. Wherever there's a refinery, that's the brand of gas and oil that you're buying, no matter what it says on the pump or can.
By the way, RichardJ, most engine wear occurs during start-up, not warm up. Once the engine has oil pressure, wear isn't much of a problem even with a cold engine, and 20w-50 does a much better job of protecting engine parts on start-up than the lighter viscosity oils. Yes, the lighter oils do build up pressure marginally quicker than the heavier ones, but the heavy oils protect from scuffing better on start-up. Six of one and a half dozen of the other kind of situation, so take your pick. The most important thing regarding oil is to change it when it gets dirty and use a good quality filter. Other than that, I think it's mostly a matter of personal preference. OK, that's my two cent's worth.
