I drive a manual so I might be able to tell a little more than an automatic drivers, but it could all be in my head so take it for what it's worth.
I installed a K&N air filter in the OEM box, and couldn't tell any difference, at lower RPMs. However, when over 3500 I could tell quicker acceleration like highway merging.
I just installed the the Airaid TBS today, and could definitely tell that it had more torque in the lower RPMs. It definitely seemed to have more pep taking off in first gear and when upshifting. Super quick and easy install too!
The whistle that some complained about is really not that loud at all. It actually sounds alittle like a turbodiesel. For cheap HP and torque I definitely recommend both of these. Both can be done for $150 including shipping.