Minimal, not a noticable difference. I only changed mine to a k&n so I never have to buy an air filter again. Just clean it, dry it, oil it and your good to go.
I decided to ditch my air box to try and get a 2nd battery in the bay. Used a spectra 6"x3" od tube and K&N cone filter from auto zone clamped to the factory rubber tube. Didnt feel a gain but it is a little bit louder