How different is the M1 SS 5W 30 from the M1 SS 10W30? My mfg recommends 10W 30 but I've been running 5W 30 for the winter where it has dipped to - 20F this week. In terms of viscosity, how much more would the 10W 30 protect the engine? I am switching back to 10W 30 this weekend. Just a bit paranoid that is all. Thanks.