All I can add to this, is when a garage recently serviced our Diesel, they forgot to reconnect the air intake pipe (yeh great I know), obviously the car was now running with no air filter. The car pulled much harder when I drove it, and on the bum dyno I gave it definate increased performance (and superb intake noise too
)
When I reconnected the pipe, it resumed usual performance IMHO.
A conclusion for myself would be that a better flowing panel filter will give better overall performance