What is interesting to note is the horsepower boost seems to be mostly on paper. Take a look at this dynograph from a 2011 N63 powered 550i with Stage I and Stage II BMS tunes. 392 wheel horsepower stock and then 448 wheel horsepower with the Stage I tune and 463 wheel horsepower with the Stage II.
Now here is a 2014 N63TU powered 550i. Keep in mind this vehicle has downpipes which do not seem to be adding power on the stock tune. The baseline is 385 wheel horsepower. With the Stage I tune, 452 wheel horsepower for a gain just under 70 wheel horsepower.
The baseline shows both motors with about the same peak power although more torque on the N63TU. Is that due to the downpipes? Possibly, but the motors are surprisingly close at the wheels despite the crank horsepower rating change. The motors are also close when tuned so it appears the N63 is not giving up much of anything to the N63TU as for now it is making more power although that is due to more boost.
We will have to see numbers from an N63TU without downpipes to see the effect they are having and have a better comparison. Additionally, it will be nice to see Stage 2 numbers with more boost on the N63TU. Those who have the N63 can rest easy knowing the addition of Valvetronic to the motor is not some huge loss for them in tuning potential and may turn out to be a benefit.