^...and really, probably the best the average joe can do(raises hand) is a UOA to see how much actual dirt got in, depending on the type of oil you used(as some oils have silicon from the bottle virgin, part of formulation or not), which is why sticking to one brand of oil for xx amount of miles with 1 air filter, then proceeding with the 2nd filter for xx miles/same oil is about as good as it gets, 2 simple UOA later...well, there you go.
The trickiest part is reading into such a UOA for what it's worth. Air filtration efficiency is even more important the longer the OCI, as shorter intervals give actual dirt/dust the chance to wash out with the drain of used oil. You are relying strictly on oil filter to get what is ingested via the engine from all sources, not just the air filter.

The trickiest part is reading into such a UOA for what it's worth. Air filtration efficiency is even more important the longer the OCI, as shorter intervals give actual dirt/dust the chance to wash out with the drain of used oil. You are relying strictly on oil filter to get what is ingested via the engine from all sources, not just the air filter.