No need to worry about momentary high revs during break-in period. I would be more worried if you keep the engine at constant engine and road speeds all the time. It is even better to give the engine some mid to high rev pulls like from 4000 to 5000 and back and repeat again, do this at least a few times during the break-in period, it helps. Stay calm with the throttle when the engine is cold (depending on outside weather, first 5 to 10 minutes of driving), before or after break-in, doesn't matter. Finally, do not switch off the engine after a long drive or pushing it hard, wait for the turbo(or turbos) to cool down a bit either by waiting at idle a few minutes or better keeping your driving calm and smooth for the last few minutes of driving before you park it.
Most importantly always secondguess whatever your sales guy tells you, every engine needs some kind of break-in but it doesn't mean babying the car.
Enjoy the car.
"The mark of a great car is one whose overall competence exceeds what you should expect from its individual components and the 1M does just that", Chris Harris.
BMW 1M-SOLD-: TECH: Evolve Race+N55mids, Evolve IC, Michelin PSS, ER cp, aFe filter, CDVx, Vorshlag camber plates, BMS OCC EXTERIOR: trunk spoiler, blacklines, black grills, IND goodies INTERIOR: Alcantara steering wheel, steel pedals, custom mats, MPower e-brake.