Replace K&N CAI with something more popular?

You should pick up 10+ HP easy or so by switching to the C&L or JLT CAI, but you will need a tune for either of those.

Yes, you will need a tune, but the benifit is great.
More power
Better throttle responce
future adjustability
and so on.

Jay

Get the JLT, and dump the k&N.

Check out this article on a cold air kit comparison for 2005 and up GT's. It was in 5.0 mustang magazine earlier this year and it should help you make your choice.

http://www.mustang50magazine.com/techarticles/m5lp_0601w_cold_air_intake/index1.html

Several tested at around 7-8 hp increase over the K&N (or only 5hp if a tune is applied to the K&N), but they require tuning, so it will cost more. You have to decide if $600 or so is worth the extra hp. I do remember reading in somewhere that the smaller size of the K&N would become a factor if you did more modifications to your car to improve breathing (ie ported heads, cm delete plates, larger throttle body, etc). All of that aside I like the Western Motorsports piece. I'll eventually upgrade to it when the warranty is up and I start hunting for more power. It doesn't provide the most power, but it looks cool and there is no way it could be a restriction to airflow.

Get a CAI/Tune combo! Its definately worth the money. Make sure you find a company that has good after sale support as well, as a good product. I had problems with mine but the support to fix it was excellent!