Both oiled gauze and oiled foam filters have been tried. The oiled foam ones have worked the best, by far. The filters are over twice the size they need to be. This way, they can clog a bit with no performance loss.
This is interesting.
We spend a considerable amount of time riding in the sand and have found the K@N filters to be superior to foam.
Sand and salt must filter differently.
That being said, currently we do run an oiled foam at Bonneville.
As far as size goes, we use as large as we can make fit.
Don