Its pretty interesting realoem states N54T for 1m/Z4 35is, and along with other websites saying the is was also tweaked by the M division.
When ppl with the 35i call out others with the 35is with a "big ego" I just chuckle. It's like the e46 328 guys saying that with an intake they'll be as fast as e46 330i.
It kinda of went both ways between supercharged 330's and M3's. Speaking for experience I can say that my supercharged 330's both beat and lost marginally to M3's. I beat an M6 on the highway.
I picked up an Z4is because IMO 335hp with engine, tranny, suspension tuning (and I think additional oil coolers) under warranty is better than a Z4 35i with a chip w/o warranty.
At the end of the day who cares. As long as we enjoy our rides.