In test I have seen but cannot remember the link, the K&N oil filter was a pretty average performer and no better or for that matter worse than any other after market filter.
I suggest that if the K&N filter is more than 50p more than any other after market oil filter you do not buy it.
With regards to the air filter it is unlikely that there will be a measurable increase in performance unless someone can post performance numbers before and after the K&N was used.
All users who purchase these items always say they can feel a difference but they would do at the price they have paid.
My Roadster didn't have an air filter ex factory just the box & the filter couldn't have fitted as the flash on the moulding made it impossible to fit.
I fitted a K&N as they are a lifetime product, perhaps they add a few BHP as well.
