Don't think the N54 - N55 thing is material regarding a CAI because base they both dyno within a few whp of each other. That being said the N54 reacts much better to tuning than the N55.
2014 BMW 435M-Sport
2013 BMW 135is 6MT conv JB4/ISO
2009 Ford Expedition 4X4 EL - 2009 V-Star
2003 Nissan Xterra 4X4 - 1998 Ford Ranger 4X4 Splash
FFR Cobra Mk-IV work in progress