Well, this is where things get a little tricky. The dyno won't (shouldn't) reflect any real change in numbers because it's done with the hood up. That being said, I'm highly curious as to how much this will or will not affect fuel mileage.
Now I will preface what I am about to say by stating that in no way am I trying to put down the K&N intake, it's design, or anything. I truly like the way it looks and the numbers are definitively better above 4.2k when compared to my current setup beyond the shadow of a doubt. I like all of the aftermarket intakes in some way, shape, or form.
That being said, I pulled my headlight and closed my hood in order to better examine the effectiveness of the setup. I couldn't get pics due to my dumb phone and lack of light, but the engine-bay air has multiple avenues to access the filter. Combined with the amount of sealing that has been done to the Mk3 engine bay, I can understand why some of the posters commented on possible heat-soak issues. Air will naturally follow the path of least resistance, so it would make sense that anyone with the setup that still has the snorkel installed will probably be paying a price for it.
With the amount of surface area that air can seep around to the filter, there *shouldn't* be much suction (if any) through the Newmission install. This is something I will be checking for once the mod is complete. What will change, however, is the temperature of the air available to the intake while the car is in motion. Time will tell, I do believe.