i just bought a 2013 550i in Sept. 400 hp.
the 550i GT got the upgrade for 2013 right away. the 550i is not getting the new horse power until the face lift hits q3 or q4. Kinda bumbed about it, but I really think its just the engine is detuned. Dinan stage 2 at 501hp and does it really matter.
Piezo direct injection may mean a smaller more acurate type of injection.