i can't honestly say that i did notice a big difference but with and exhaust and other mods it would have to do sumthing.
at work we have this k & n display machine....its designed to show the difference between ryco filters and k&n ones.
the machine itself consists of two fans and a box, the fans suck air through the front, where you put the filter u wish to test, the air is then push up a vertical tube in which is a ping pong ball.
when there is no filter on the front panel the ball goes to the top of its tube, eg zero restriction. when a ryco or valvoline filter is but on the box the ball suprisingly drops all the way to the bottom of the tube, eg ****e loads of restriction. with the k&n filter on the ball will return to the top of the tube, idicating that there is basically no restriction of air flow with the k&n filters.
this machine really does show that the filter must benefit the effiency of the intake of your car but if it isn't designed to suck in that volume of air the the k&n filters allow then really its of no benefit. however there should be some gains in a standard engine in responsiveness. i did notice this to some extent but not as much as i had hoped.
hope that helps troy
cheers
ryan