“just monitor the oil level ... because it is Mobil 1. I have found that for some reason Mobil 1 burns off a bit easier than other synthetics of the same weight in air cooled engines.”
I have experienced this as well. I have always thought this was because, traditionally, Mobil 1 starts out on the thin side of each weight to achieve a bit of extra power and efficiency. I can't say that this is still the case, as I haven't seen a VOA in a few years … but I bet it is as this has been the industry trend for the last decade or more.
”I am definitely a fan of running the thickest oil allowed … I assume this would be for a mower? At that point, why not run a 20W-50?”
An unnecessarily thick oil will rob your engine of power … and for splash-lubed engines, the thicker oil may not 'splash' properly, with oil failing to reach critical areas in sufficient quantity to properly protect the metal. With higher temps (say, Florida and the southwest of the U.S.) the oil will thin at extreme temps and that may well be the way to go. Cujet swears by Mobil 1 15W-50 for OPE in his neck of the woods.
But for Minnesota, Wisconsin or Upstate N.Y. Where extremely temps are rare, lighter weights are usually the order of the day. I would use 15W-40 in a lawn mower, only (strictly summer use). All other OPE gets a XW30, depending, depending.