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.
2007 E92 6MT - Silverstone II with /// Performance Exhaust with ACM Test Pipes and BPM Sport Stage II Dev-Tune
2011 F25 X3 3.0d