Hi,
just sharing my experience with my Swift with the K&N filter over the last few weeks. Peak power has not changed significantly. However, being a Swift, that was never needed. In gear acceleration has, however, improved significantly. You know that the K series engine in the Swift produces a surge of power after 2500rpm. However, with the K&N filter, the power delivery has become more linear, so I have the punch in gear at any rpm. Overtaking is as easy as pointing your car in the required gap and driving there. This coming from a generally sedate driver - I never push to 100% and prefer to drive smoothly rather than aggressively
Ameyam