I would have to say yes that I have noticed a little difference. The engine will now run to 5,200 rpm and used to run to about 5,050 and when I open the hatch while the engine's running it doesn't sound like a vacuum cleaner any longer.
PLUS++++++ : The K&N Filter looks cool on the front of the engine. It was the first thing that Karen noticed a few weeks ago when we went for our first ride of the season and I had the hatch open for the first few minutes of our shake down cruise.
It's basically the same filter that's used on the HP500 EFI's since the throttle body diameters are exactly the same.