Ive been using finer filter on my 4d56T for almost a year, no encountered problems of anykind.
Just be sure to follow cleaning schedules religiously youll be fine.
It is recommended on the instructions that came with it to Clean every 15000 but i clean mine every 5000.
also dont forget to give it a visual inspection from time to time maybe every 2tk or so just to be sure that it wouldnt dry up (baka daw kasi magpulbos and mahigop ng engine)

in terms of performance own observation ko lang, i felt my engine became more responsive or psychological maybe? well parehong pareho lang ng k&n coz ive also used this before on the same vehicle.
mas maganda lang ang tunog ng k&n at the same time mas maganda ang price heheh