Since you are tuning go N54. I traded in my 2011 335i N55 for a 2012 335is N54 in July just to get the N54 platform.
I had my N55 with a Procede, Intake, DP, and was not happy about the performance yields.
2008 335xi E90 Alpine White - Sold - 8/19/10
> 2011 335xi E90 Jet Black - Sold - 6/27/12 > 2012 335IS E92 Crimson Red - Current