Well Tim 40*C and 100*C are two numbers used in the oil industry. If an oil is flowing better at 40*C it is flowing better at 10*C and even lower, so it is doing its job better at colder temps as in freezing and below, all the way up to operating temps. At every tick of the thermometer on up till it reaches operating temps.
In the winter it can take 20 minutes or more to reach operating temps. I've read that a million times before so it is pretty common. The three oils I mentioned were developed for Hybrid cars which are started and stopped frequently and are hard on engines because of that. They were also developed for 5W20 applications offering better cold protection, so it is a big deal IMO. An oil that has a Viscosity of 38 cST at 40C is better for cold protection than one that has a Viscosity of 49 cST at 40C. That 38 cST oil will get to the desired operating viscosity faster too.
Just wondering this is off Amsoil's site why is it they use a certain set of numbers when testing ASM, then different numbers for testing SSO? Speed and temps are different, IIRC a slower speed is harder on this worthless for testing oil test.
Four Ball Wear, 75°C, 1200 rpm, 40kg, 1 hour (ASTM D-4172B)
Four-Ball Wear Test (ASTM D4172: 40kgf, 150°C, 1800 rpm, 1 hr) Scar diameter, mm 0.406