Got the filter at Auto Zone. Not many carry this so you might just start calling around. the K & N Part Number is 33-2128. Comes ready to install w/instructions. You are probably already familiar with their product but just in case, the filter's last forever, require cleaning and new spay on oil every 50,000 miles. The new filter will come pre-oiled so you won't have to buy a cleaning kit for some time.
Honestly, I can't tell if the car has any more torque or Horse Power. Kinda like Chicken Soup for a cold, can't hurt. As far the sound, I can tell the difference when I get above 3500 rpm.
I've been reading about some Cat Back Stainless Steel Pipes/exhaust system. I can only believe they would improve performance. Just not ready to spend a thousand bucks on them. The dealer said if I replace the stock exhaust with the Cat Back units, it would only effect that part of the warranty.