I seriously doubt Dinan's gains will be the same on the N63Tu engine as compared to the N63. Valvetronic is a high tech valve-lift based throttling system. By itself, it does very little actually increase HP. It does reduce pumping losses and intake pressure surging thereby improving throttle response and emissions (and perhaps a little efficiency but who cares). My guess is the bulk of the HP increase on the Tu comes from increased boost, which is all that Dinan is doing (along with the necessary remapping of fuel, spark and cam timing). The question is how much boost can the N63/N62Tu take without risking reliability (best case) or damage (worst case).
As SD said, theres also the question of how much torque can the rest of the drivetrain can tolerate. Southy was basically correct in his statement that BMW did what Dinan does - raise the boost. I am also of the opinion that like most BMW engines, the N63 is stronger than the marketing info suggests. My estimate is 420HP for the N63. I haven't looked into the Tu yet. Perhaps some of the increase is simply a more accurate publication of its HP.