EDIT: Note this post is for the N54 twin turbo motor!
Well, finally getting around to posting this.
I had started to experience some misfire and timing correction with only 30k on the clock. After uninstalling my Cobb AP and taking it to the dealer it seemed to stop occurring. I put the Cobb back on but only on the lowest tune setting which ran fine.
After some research, I decided to pick up a new set of plugs and get the Bosch part (ZGR6STE2).
Plug tool:
http://www.amazon.com/gp/product/B002YK78VI
Plugs:
http://www.amazon.com/gp/product/B001C5Y3ZA
I won't regurgitate the DIY on plugs, but wanted to share pictures showing how far worn my plugs were with so few miles. This is consistent with others reporting short spark plug intervals with tunes.
After examination, I have to side with the "the Bosch ZGR6STE2 is the same as the BMW branded plug" thought process. I know some people thought there were differences. Yeah, you might spot some tiny differences, but I really do feel they are the same plug.
Rest of pics are the old ones compared to new so you can see the wear they encountered.
I had two oddities in the plugs worth noting. On plug 1, one of the three grounds was fairly black on the back side, while the other two grounds and all other 5 plugs were yellow/white. It's not that significant.
https://dl.dropbox.com/u/27624835/ca.../plug1_002.jpg
Of note, the center electrode was worn into a soft triangular shape. Look at the wear difference! Wow.
Onto plug 2:
And 3:
The other notable thing is plug 5 had what appears to be a small amount of oil in the threads.
There was no visible oil in the plug galley, but I'm slightly concerned about it. I think I'll pull cylinder 5 again in a few thousand miles and see if it repeats.
I had a hard time using my dial calipers to measure the gap and normal gap feelers do not work, but some measuring pixels in photoshop shows about a 70% larger gap in my used plugs with ~35k compared to the new ZGR6STE2 plugs.
Just nuts. I changed the more typical single ground on top of electrode-style iridium plugs in my STI after 40k and they had virtually no wear. Not sure the reason, but I guess direct injection?
I haven't put the aggressive Cobb tune back on, but there is an immediate difference in power and response. I think I'll give these new plugs a max of 20k before replacement, if not sooner.