Interesting.
I had a misfire in cylinder #3 on my E90 with the N51 at 40k miles or so. It ended up being a bad coil (swapped the coil and the issue followed the coil) but I also replaced the plugs at the same time, and they were smoked.
I've read the N51 is harder on plugs for some reason. Not sure if that is true, but mine were definitely due by 40k miles and were factory OE. Meanwhile I did the plugs in a friend's 2006 N52 and at 130k miles they still looked decent.
