All the comparison tests I have seen show that the K & N and similar (oiled cotton) type filters allow a higher proportion of smaller particles to pass through them. My own experience backs this up I was riding with two guys who had identical bikes in dusty conditions. After a thousand miles or so the bike with the standard filter lost power and started to run very rich because the filter became blocked. The other bike was still running OK but we checked the filter anyway. It was not a K&N but similar in that it was an oiled cotton filter, it was dirty and you could see a fine dust layer on the carburetor side of the filter showing dust had got past it and into the engine. We cleaned the OEM filter with compressed air and the bike ran fine but it did need cleaning again in less than a 1000 miles. I had a foam filter on that trip it did not need cleaning and no dust got past it.
For longer trips I prefer to have a filter which it is cleanable rather than carry or try and locate a replacement. I think oiled foam filters are the best option. If I could not get a foam filter I would use a OEM paper filter rather than a K&N.
One thing to watch out for when cleaning paper filters with compressed air is make certain the air is dry and don’t use too much pressure as it can open up the filter weave, which will allow fine dust to pass.