BMW is basically rating the motor at the wheels what it is showing at the crank. They are playing the German horsepower war conservatively and keeping numbers low for the sake of competition and delivering them where they matter, at the tire. That way they do not get caught up in a power shootout on paper which Mercedes loves to do.
The peak torque figure exceeds the peak horsepower figure which is interesting as the quoted torque figure is less than the quoted horsepower figure at 406 lb-ft of torque. The torque curve itself is not BMW M's best work but it is certainly flatter through the curve than the N54 and N55. It drops off toward redline as expected but it holds past 7000 rpm enough for the HP curve to not take a big dive. This is the best looking curve of a turbocharged M motor to this point.
What about the tuned numbers? They take the M3 up to 479 wheel horsepower and 484 lb-ft of wheel torque. Roughly 52 wheel horsepower gained with a mild tune early on. This tune will develop but off the showroom floor if you want another 50 horsepower at the wheels you can get it on pump gas right now without anything else needed. This is just a guess but BimmerBoost would argue that it looks like ~500 whp for tuned S55 motors on pump gas will be the norm with basic supporting mods.
BMW disappointed people with their crank horsepower ratings but did the smart thing overall. Why quote some big number when they know Mercedes and Audi both have a bit of displacement on them?
BimmerBoost would also at this time like to point out its guess from last year as to the power output of the new M3 and the S55 inline-6:
The only bright side BimmerBoost can see is that the new M3 may be severely underrated just like the F10 M5. Let's assume this is the case and apply what we have all seen with the F10 M5 to the new M3. That would mean 417 wheel horsepower for the new M3 despite its appallingly low crank rating. That would also mean an increase of 67 wheel horsepower over the E92 M3 which is a hell of a lot better than 30 horsepower at the crank.
Not a bad guess, eh?