I have the KB kit on my T-Type. It is worth a good 2mph in the heat. Removing the filter gave me no increase in MPH in my T or 10 second GN. If you have a good flowing K&N, it shouldn't be worth anything by removing it. If the car does pick up some MPH, then that should be an indication your filter is too small.
One thing I did do with the cannister is trim the top part off where it necks down to meet the filter. I then pop riveted a plastic ring so about 3" tall so it would extend past the filter. This made a looser fit. It helps so if you ever have to remove the MAF pipe from the car, you don't have to dismantle the cannister, etc.
This kit is NOT a ram air kit. That is a deceiving name as you really can't "ram" this engine. What the kit DOES do it pick up air from outside the engine compartment. No matter how hot it is outside it is always cooler than your underhood temp. Anytime an engine can breath cooler air it is definately better.