I think K&N have the edge because they are not as good at filtering, an air filter as its name suggests has to filter sh*t out of the air without restricting air flow, a contradictory task. K&N I think were developed for racing cars running in fairly clean air where as piperx were developed for motorbikes especially motx and rally cars where the air is dirty. What is more important to you, a longer engine life (piperx) or slightly better air flow and performance (K&N) unless you are in a dusty area K&N should be fine.