I'd be interested if anyone has ever pulled a valve cover off an engine, and timed how long it took various weight oils, before they reached the top end of the engine? (Rocker arms and such). After sitting overnight in below zero weather.
Nothing too scientific. Just start the engine in below zero weather, and time it with a stopwatch. 0W-20, 0W-30, 10W-40, etc. That would be good to know. Also if they could check the various cranking RPM's as well with these different weight oils. That is information that could be useful to guys like the OP, who are trying to select the proper weight oil to suit his cold weather requirements.
An old member named BuickGN and I did that years ago during the BITOG straight grade wars. Delo 400 SAE30 was on clearance for $.99/gallon and I bought a ton. The discussion was that straight grades did not flow well enough to lubricate an OHV engine below freezing.
I used my trail Jeep in my sig and pulled the valve cover off the AMC 2.5L 4 popper and started her up on a low 20-somthing degree day. Sure enough, oil immediately flowed from every rocker. I believe BuickGN did it with his favorite 20W50 with the same results.
Absolutely no scientific method used at all, just backyard "I see oil, it's good". I don't recall any difference in cranking sound but if there was, it was likely the drag of the 80W90 gear oil in the Muncie SM420 granny low transmission because it was started in neutral.