After working in my father-in-laws compressor biz for 10 years, (20 years ago

) we always used 30w non-detergent.
With that being said, our temps don't have the vast change that some parts of the country have, not to mention great strides in technology in lubricants.
In my opinion, splash lubricated pumps should always use 30w non-detergent. I have never seen any mechanical benefit to using anything but. Pressure fed pumps might see advantages, but I would have to see the insides after several years of use to completely agree with its use.
After all, some of the most desired compressors are older, and have been running on the old fashioned stuff since day one.Doesn't it all come back to proper care..(regular maintenance)..anyway?