Makita air compressor all weather oil?

I replaced my oil-less air compressor that broke within a few years with a Makita MAC2400 oil lubed air compressor. It is 2.5hp, 4.2 gallon.
Here is a chart describing the oil requirements in a variety of weather from the Makita manual:
Makita MAC2400 oil.jpg

I would ideally like to just change out the ISO 68 mineral oil with something synthetic and just run the same oil year round. Per the chart SAE 20W ISO 68 oil covers most of my weather, but not all. I live in Connecticut so it definitely goes above 78F in the summer, but not usually more than the 90's. I wouldn't want to run SAE 10W in the winter because it can be single digits one week and in the 40's or 50's another week.
The compressor would stay in an un-heated garage where it will see all kinds of temperatures. The use is only for filling tires(4 cars in use here) and occasionally blowing something off for projects being worked on. So the compressor will not see much use, and I think it would be a waste to change the oil 2 or 3 times a year for so little use.
The Makita oil it came with is 20W/ISO68. It has a pour point of 0F.
Makita oil datasheet
Amsoil 20W is ISO 46, pour point -53F and I don't know why the ISO rating is different from the 20W Makita oil. Can someone explain?
Amsoil 30W ISO 68 has a 40C viscosity of 68 like the Makita oil, but Amsoil 30W is not available in low quantities. 10.5 visc @100C. Pour Point -40F.
Amsoil datasheet
Red Line PolyComp compressor oil is available in 20W ISO 68, 66 viscosity @ 40C, 8.6 visc @ 100C, -50F pour point. It is PAO & Poly Ester.
Red Line datasheet

I feel inclined to try Red Line 20W and run it in all weather, but wondering what everyone thinks. I suppose I could also mix Amsoil 20W ISO 46 & 30/40W ISO100, since they are both available in quart bottles.
I've also seen that some people use Mobil 1 automotive oil in their compressors.
The Makita manual states the below on multi-viscosity oils:
"CAUTION: Multi-Viscosity motor
oils, like 10W 30, should not be
used in an air compressor. They
leave carbon deposits on critical
components, thus reducing
performance and compressor
life. Use air compressor oil only."

Thank you
ps. Please note that I am not that knowledgeable on what specs are important in compressor like pour point, 40c visc, 100c visc, etc.
I run the Amsoil ISO 46 in my compressor and in same intended use as you do I myself would run it in the unit yearly as I intended to. Winter start up on it is excellent if it was for hard use I would use the ISO 68 or 100. I think you will be more than fine with the 46 just my opinion.
Admittedly my compressor is not a Makita, but it is a belt driven 2 cylinder compressor that called for 10w40 from the factory, and I have used that or 10w30 in either conventional, or semi synthetic, or full synthetic, for the last 30 years, and I use it more than you do, and it still works good, although for the last couple years it is using a little oil. I usually change it every year, but have gone to every other year, as I don't use it much after I retired,
I've been running Rotella T5 15W40 in exactly same compressor for 5 years no ill effects.... (reason for this particular oil - got lots of it on hand)
The compressor is used for rough carpentry work if that helps.
Jupiter, Florida
I have the Makita 5200 "big bore" 3hp compressor in our unheated T hangar in upstate NY. It does struggle to start when cold. Sometimes it pops its own breaker. I'm quite sure a thinner oil would help.