Two VERY important points to note from this test...
#1 the test was only conducted for 500 miles, most filters recommend changes at 7500-25000 miles.
#2 (related to #1) this test does not address dirt holding capacity of the filter media what-so-ever, which is a HUGE factor in the long term performance of a filter. I know for a fact that foam and gauze filters will filter better as they get dirtier.
Also, if you look closely, 2 of the 3 foam filters flowed within 3% of the K&N filter, yet Bob said they only flowed "marginally better" than paper. In reality, the Amsoil filter performed within 1.5%. (Paper flow was within 7% of K&N flow.)
The problems with BOB's test are numerous (I, myself am an Astronautical engineer), but as I've seen even in my own circles, carelessness with test results can lead to drastically different conclusions.
Again, I don't want to "beat BOB up", but anyone ever notice that within 5 minutes after changing the oil in a diesel engine, the oil is black? Does that mean it needs to be changed immediately? No, the soot in diesel oil is smaller than 1 micron in size and no threat to the engine whatsoever, but looks pretty disturbing. Point? Without analysis of the size of the dirt particles, and test controls over which day was dustier and what kind of dust was encountered, further ?'s arise.
In the end, I agree with SavageRob. Do some research and decide for yourself. My own experience and research have indicated to me, that over the life expectancy of an air filter, foam can't be beat. On the other hand, I agree with Bob...when it comes time to clean the foam or gauze filter, a paper filter looks pretty appealing.
One thing that has not been researched/tested to my knowledge is: what size dirt particles injested thru the intake cause the majority of engine wear. (Extensive testing has been done in this area with engine oil, and the answer is 5-25 micron dirt particles account for 50% or more of the engine wear on an internal combustion engine.)