Read a ton about anything before deciding you can make your BMW better. There are many unanticipated consequences to just slapping a different part in. All I've read saying there's what you have or the BMW perf. intake...and also, from what I've read, you will only notice if you do lots of other stuff...and then, you might build up another little bit of modest hp.
I'm conservative with regards engineering automobiles. I think that since I'm not as knowledgeable as the BMW engineers, I should defer to their decisions.
Intake? Just get a really good one designed for the car. I'm not liking the CAI so much, I have to say, nor KnN reusable filters all based on what I've read here.
If you're looking into intakes, be sure to study until you start to hear vacuum
leaks in your head.