If it is specified by the manufacturer, then I would continue to use it. The manufacturer has the most to loose if the filter is not adequate. Someone eluded to some "scientific" test, however just because it was done in a lab doesn't make it scientific. It is dependent on the type of "dust" used for the test, and if it is typical of what is commonly found in the air. Dust in air is going to have a huge variance in particle size. Unless the dust they chose to use had the same amount of variance as typical air quality, the test ends up being completely bogus compared to the real world. Stated differently, if typical air quality only had .0001% dust smaller than X microns, and the filter only works down to X microns, who cares, the filter is going to do its job very well.
BTW:If I put a paper filter on my engine, it peaks out at 4800 RPM and is loosing power well below that. Otherwise it easily screams to 5200 RPM.