There's a large difference between lubricated and dry air filters.
No, the DATA show that the difference in "airflow restriction" between
a NAPA paper filter and K&N is a virtually unmeasurable 1.25 millibars!
The DATA also show that the difference in restriction between the OEM
Mazda filter and no filter at all
was a similarly microscopic 3.5 millibars.
(That's equivalent to the delta-P for a 100 foot change in elevation.)
Forthermore, that's ONLY at wide-open-throttle. At any other operating
condition, the difference in filter pressure drops is even less _AND_ the
total atmosphere-to-cylinder flow restriction is TOTALLY INDEPENDENT
of the air filter design (including no air filter at all).
At other than wide-open-throttle conditions, any reduction in delta-P
across the air filter is exactly
cancelled out by an equal-but-opposite
increase in delta-P across the (partially closed) throttlebody butterfly.
The pistons don't care
what's limiting the airflow when the driver isn't
calling for balls-to-the-wall maximum power.
...happily, physics is immune to the placebo effect,