K&Ns don't always flow more air than stock. Case in point, my friend's 2009 ZX-6R lost power. With a full Two Brothers system, their Juice Box with their map and the stock air filter he was up 1 bhp (with significant midrange gains). Dropped in a K&N (same dyno, same day) and lost his midrange gains and 2 bhp at peak, which put him below stock output. In other words, the filter flowed less air than stock and voided the pipe and fuel module. Other tuners I know have seen the same thing.
In my mind, the greatest advantage of a K&N is that it has superior filtering capabilities due to the dust-attracting properties of the oiled gauze, and they are washable and infinitely reusable. For those reasons they are a great street filter, but on a race bike or other machine where peak performance is desire, I'd go with a Pipercross or some other filter (like DNA) that can show me that for THAT particular filter their version flows more air.