I DO like 5w20, but as my owners manual calls for, 5w20 is to be used only if the ouside air temp does not rise ABOVE 0 F. Even in my colder than most part of the world, it isn't that cold all the time in the winter! I'm much more comfortable with the 5w30 under 60 F recommendation, and it seems to work well in the winter!
For this engine, I can't imagine putting a 5w20 in there - just too old of an engine design for that to work well, IMHO.
Wasn't cool yesterday or today. 97 yesterday, and 90 ish today with a boatload of humidity. Supposed to be back to lows in the mid forties over labor day weekend - back to good sleeping weather!