I have put about 2000 miles on the 456 since I took the wadding out of the airboxes and after taking them apart again for other maintenance I can say the filter is not dirty at all. A couple of other points: There is a slight increase in intake noise as was previously noted - not bothersome to me at all. I spread grease on the screen I re-installed without the filter element, as well as on the sides of the inlet tubing. This is effective (much like the mucus in your nose/throat) at picking up stuff before it hits the filter. There was some dust/sand/bugs on these areas, but not excessive. I have driven a fair bit in the rain with some heavy downpours with the last being a few days prior to the maintenance and both filters were dry, as was the airbox; not a drop of moisture in sight. As to different types of airfilters and performance: Being that the engine is an airpump, more air (provided the fueling is correct) will mean more power. There is a simple way to measure this - the MAF. I was troubleshooting a part throttle issue with the car and I was monitoring the MAF output voltage to the ECU. It is a voltage signal proportional to flow. I did back to back full throttle runs with the filter and without, with no appreciable change (less than 1% change) in voltage/flow. If this is the difference with the filter and without, a "better" filter will not give you a gain worth anything. [note that I repeated the runs a few times using a digital multimeter and I do not claim the experiment was perfect; it is the lack of any difference between filter/no filter that leads me to believe the stock setup is probably pretty low in terms of pressure drop and it is unlikely a filter with a lower pressure drop will provide a discernable difference] I toyed with the idea of repeating this testing with the MAF screens removed/in place, as there are many claims that these are a source of flow restriction as well, but these I would say are likely less restrictive than the filter... An enterprising person may want to experiment with a manometer to see what the pressure is in the airbox below the filter at speed compared with that in the upper airbox and down stream of the MAF. This would give one a better understanding of the filter/MAF performance in terms of flow restriction.