Honest answer. Will having a K & N filter impact performance that much if a jet kit hasn't been installed? I've seen posts stating opinions on both sides, here and other places.

What's the fact? What symptoms would appear?

 

Only if you gut the airbox and go with pod filters. Otherwise you will get some improved flow over stock but not enough to require rejetting. The big deal with K&N is lifetime filter and superior flow even when dirty.