High altitude means reduced NA engine power.... requiring more gas pedal to move that asphyxiating vehicle. At 9200, you're losing ~1/4 of the engine power, or the equivalent of shrinking the engine by ~25-30% and effectively moving air/fuel comparable to a ~1.7-1.9L engine at sea-level. Big engine making little power burning little fuel(engine adapts A/F to o2 sensor readings).... pushed harder.... should hopefully reduce fuel diluting oil, but fuel diluting oil might also be exaggerated by short trips.
You don't need a pcv valve to vent a crankcase.
What an engine tolerates for overfill depends on the specific engine.. there is no such thing as 'most'.
1. It is not expected to have fuel leak past the rings. That would be bad engineering or excessive blowby compression lost from wear/tear and ineffective rings(crud/wear/carbon), and poor fuel spray pattern(cheap fuel and no injector cleaner usage). Avoid excessive short trips and get it all warmed up.
2. Oil is saturated from excessive short trips and driving like a snowflake. Fuel evaporates from the oil continuously. Some driving styles add more fuel than can be evaporated.
I don't use a scan tool for a compression test or leakdown test. Too many here don't have a clue.
I don't see the point of siphoning oil. If its that bad, change the oil and filter, and change the PCV valve regularly, like every 30k miles.
Octane is used for detonation control. In the winter, on an NA engine, you don't need as much octane as you would in a hot summer environment. If octane isn't sufficient, engine tuning will adjust any one or combination of cylinder pressure, timing, and fuel ratio to adapt, which could increase oil dilution from excessive fuel injected or not enough time for that fuel to burn or not enough heat to burn the fuel.
Idiocracy is alive in this thread. I thing we have too many clueless blabbering with each other above. Its laughable.
The wife is a 99% city driver and makes oil level and plenty of it. So, this properly engineering and running engine needs me to take it on 1 of my highway commutes every couple weeks to remove that pint-quart of fuel... Highways here run 80mph+ in a 70mph zone and 1 trip drops the oil level drastically and it isn't oil consumption.
I'd wager the negligent owners, short trippers, cheap fuel or oil users, and hypermilers... will have more issues than someone that overmaintains the vehicle with quality fuel/lubes and drives with some enthusiasm.