This may help a bit:
https://www.widman.biz/English/Tables/gr-motores.html

The single grade oils have a different temperature dependency than the multigrade oils. They're not 1:1 comparable and the curves are not linear. A multigrade oil is always a compromise to fulfill all the needs. This can be achieved by adding additives. The more required the higher the specs and the more expensive the oil gets

Thomas

I didn't write that synthetic oils won't have them at all. They don't have them by nature, so they require adding them by the blend. Problem is that they're mostly not dosed high enough to let all seals swell as required in an aircooled 911.

Thomas

It's true that engine oils are required to warm up to a "working temperature" where they can burn fuel and combustion-by products and evaporate water (coming from cold running phase by enriched mixtures, fuels are hydro carbons). But the temperature interval is not that narrow as you denoted.

https://i.imgur.com/BzA2AGD.png
Source:
https://www.wearcheck.co.za/shared/TB43.pdf

Of course this graph does not represent every oil and every engine, but it gives a good impression on which temperatures we're talking and when what happens. Here is a watercooled engine in regard, they have due to the water cooling circulation a very even temperature distribution overall. An aircooled engine has in contradiction a more diverse temperature distribution, some areas may be much hotter than others, in summary the oil temperature of an aircooled engine shows us the tendency of the engine temperature of this engine overall. So based on the graph we can conclude that oil temperatures above ~72°C / 165°F will start the process of burning fuel and combustion residues and evaporating water from it. Higher temperatures will supoprt this, but temperatures way higher than 90-100°C / 198-216°F does not help any further on this, but will have the negative effects on viscosity and lubrication.

Thomas

Great comments all. That said, and as someone else noted, most modern synthetics have additives now that help seals swell. Especially high mileage synthetics.

Not true. Anything above about 185F will steam off the moisture. As an experiment turn a pot on the stove and heat it up to a boil. You will see steam coming out before 185F if memory serves, and a lot of steam will be coming off well before boiling. Now the cooler the oil temp (closer to 185F let’s say) the longer it will take. So if you only do short trips, and dont get your oil up to operating temp for 20 min or more, you will never burn off the moisture.

Thats why cars that sit all year, or are barely driven during a year, esp in a climate like Florida (currently 84F and 60% humidity), need their oil changes yearly regardless. Take your car for a 20 min freeway drive though and the water is gone. I make sure to give every one of my air cooled cars a 20 min freeway cruise (20 min after the oil is up to temp) ever other month minimum.

On a nice 60deg day, measured the 3.2 exhaust temps at the heads all within 5-10% in the high 300s under 400.

Re: removal of water from the oil ... another factor to keep in mind is that your gauge is measuring the "cold" side of the oil system (post external cooler, if you have one). So if your gauge says 210, the oil in the bottom of your crankcase, is probably 20+ deg F hotter. And there is lots of turbulence and movement of air to carry away condensation out the vent at the top of the engine. As someone stated above, once your engine reaches operating temp of 180 F, there should be a good amount of evaporation happening. Personally I think aircooled engines are better off staying cool, rather than pushing the temperature capabilities of whatever oil you're using.

Thermostat and a big cooler
 

I am a firm believer in running a big front/fender cooler and let the thermostat control the cooling temps. Having the oil temps get too high and engine parts, like valve guides start to wear more quickly.

You could experience big oil temps at track days or a vacation through hot country, or just blazing through the mountains.

Safer with excess cooling capacity, particularly considering the eyewatering cost of a rebuild.
c

When I built my engine I talked with Charles Navarro of L&N Engineering who makes the "Nickies" cylinders. His design has more cooling fins and is said to lower operating temperatures. He said I should run this oil in his products.
https://www.drivenracingoil.com/products/gp-1-20w-50-synthetic-blend-high-performance-oil
It seems to me to be slipperier than full synthetic when I get it on my hands and try to pick up tools?
He said it would drop the oil temps by 10-20*
YMMV.