Under questioning a Lycoming service rep once admitted that too thin
oil is probably much less damaging than too thick oil.

There was a Texas twin many years ago at Aspen that left with a
cylinder preheat and start with 50 weight oil on a cold morning. Both
engines shelled out on takeoff & all were killed (or so the story
went).

Don't plan on ever starting it with 50 weight oil under about 50 deg F
oil temp.

The problem isn't starting. It's getting an adequate fog or spray of
lubrication going inside the crankcase. A lot of things go against you
with thicker oil. On top of that, oil that blows over the oil pump
relief valve doesn't really have access to the hot areas of the engine.
At least that's my take on flying to colder areas.