From my Dyno runs, the K&N produced a slightly richer A/F mixture and about a half to one hp less. I would have to hunt the charts down to give exact numbers. The K&N that I tried came from SiSF's bike, BTW, from back in his K&N days. As a bonus, the K&N will also let more dirt into your engine and possibly deform the airbox. All for only sixty odd dollars. What a deal. What's not to like?
I had a K&N once. Then I held it up to the light...