335i owner here. I've been following the dyno stuff for a long time on e90post.com. I belive the consensus is a 12-13% drivetrain loss for the manual transmission cars and 15% for the automatics.
Benchmarks may be a better comparision since dynos will vary based upon so many factors (weather conditions, what type of dyno it is, the fuel used, etc). Multiple magazines have had the 335i trap at 103-105 MPH, about 1 MPH slower than the 150 lb lighter E46 M3 with 333 HP. Most believe a stock 335i makes somewhere between 320 and 340 HP.
The easy tunability, huge powerband (1400 RPM to 6200 RPM), smoothness, efficiency, and great sound of this inline six make it well deserving of the 2007 Engine of the Year Award it recently won.
Driving sideways: It's not faster, but damn it's more fun!