This came up earlier this year on the Early S website and I did some dyno testing to try to get a definitive answer. The results were that on my 2.2S motor the factory intake system made more power from 3,200 rpm - 6,600 rpm than the K&N filters. At higher and lower RPM's the K&N's were better. There does seem to be evidence to support the argument the stock intake is resonance tuned to stregthen the midrange. That being said, I still run the K&N's because I think the inprovement in sound outweighs the slight loss of power.
Check out the thread for full discussion and dyno charts. Also tested sport vs. stock mufflers while I was at it.
http://d240157.u39.zeonhost.com/for...read.php?t=4752
Brooke