Some light information you should know when it comes to best filters available at the moment. This is in order of best to fair, its dyno proven with their reference taken from dyno run without a filter 155kw.
1. HKS racing pod style filter (compact) 153.9kw
2. K&N rampod with slong snout. 153.7kw
3. Simota Rampod 153.3kw
4. Finer Filter ......~151
Couldnt remember the other filters.
Oh yes the ever popular Rush filters ummmm found to be one of the restrictive at 149kw when dynoed.
Oh Source of this information - Hot4s, yes I know shame on me, but mate from work had copy sitting on the table.
Hope this information will help you all gain that extra couple of kw's.