With the change of air filter, the bike will require a proper 'tuning' to be done. Tuning - there are two areas, one is the syn of all 4 of the carb, the other is the air/fuel ratio.
Without proper tuning done, the difference cannot be feel and in some cases, it will perform even worst than stock air filter coz ur bike will be running leaner with better air flow, while the fuel intake remains the same.
There is definitely increase in performance. It's whether one is able to feel it or not. And if one is expecting miracle to happen (sorta like expecting a 400cc bike to suddenly perform like a 1000cc bike), of coz it will never happen. Be practical in ur expectation.
Lastly, not too sure myself too but I believe the performance will come in very obvious on the high-end portion, whereby air flow must be fast enuf to keep smooth combustion cycle, thus K&N air filter comes into picture. Low-end wise, difference may not even be noticeable.