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I can't comment on the BMS JB4 but many people on here seem to have good experiences with it. I had the stage 1 tune from BMS and didn't like it. The power delivery was all over the place. I currently have the Dinan stage 2 software. The power doesn't feel that much more than stock but there's definitely a bump. Zero throttle or power issues. Feels like stock plus.
Charge pipe upgrade is a must on N55. Mine went while I was under warranty and the dealer said it's a wear/tear item and wouldn't cover it.
As far as exhaust, there aren't many direct bolt-on options for our cars. You could use the BMW PE or Dinan from the 135 which will require slight modification but it is totally doable. I had the Active Gen II exhaust and there was just too much resonance for me despite AA saying "no drone." I ended up doing a secondary cat and resonator delete with stock muffler. Sounds good enough for me.
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