Interesting read. I just installed the BMC filter in my '07 M3 which already had the EU filter. I noticed the BMC filter was at least 10mm short. I haven't noticed any change to the induction noise, but with the BPM Sport aka Benvo tune, I do feel the car rev much freely. I just feel it ... don't know whether this is the placebo effect. But I am enjoying the new found driving experience.
E92 M3 2007 - ///PE with Test Pipes and BPM Stage II; CF Interior & Splitters; CIC with Connected Drive