... I want the best protection for my engine.
When it goes to cold starts (or any time), that's going to be relatively hard to answer. As thin as is possible but as thick as is necessary is the short answer. As you're well aware, engines last a very long time on a wide range of viscosity choices. Of course, here, we're always trying to optimize this and choose the best of that.
For starts in the really, really cold conditions, we simply don't have the tools to determine whether a mix would pump where a fully formulated oil would not. For the fully formulated oil, we do know it meets a certain minimum score, and maybe have even more info on a data sheet. With a mix, we are a little more in the dark.
0w-20, 5w-20, 0w-30, 5w-30, 10w-30, 0w-40, 5w-40, and 15w-40 and so forth are all fantastic oils and many, many engines out there will run on any one of those grabbed at random and have no statistically significant difference in engine life.
In your vehicle, M1's 0w-20 or 0w-30 would do just fine. If I was in your shoes, I'd pretty much have to flip a coin. It would have to be a three sided coin, though, to include a 5w-30 conventional.
I have a mixing phobia, so I can't give you a real, unbiased answer on that in any case.