ever see the inside of a K&N oil filter? they do nothing, just like their air filters, you get pretend power because of less filtration. i can understand using the K&N oil filters on ej25 engines where they're in between the exhaust runners and changing the filter is like playing the game operation, the added nut i mean, but on the new ones where the filter is up top, just stick with oem or something similar.
Check the thread I started on the upside down oil filter (in fact, your question spaked that thought). Sounds like the check valve is in the filter so make sure that the K&N filter has such a valve. if it doesn't, you'll be causing much more engine wear than you would with the stock filter.
I also concur with the other poster that you really gain nothing with K&N.