Personally, I am a believer in a hard break in once everything has come up to temp. The first couple hundred miles is where everything is going to wear clear & set up. In fact, the GTR's engine is red lined from the factory for a full 10 minutes straight. Yes I know the Z does not have a clean room build motor like the GTRs , but you are not red lining for 10 minutes straight either. I have done hard break ins on all my vehicles, bikes trucks & cars with good results.
Here is an article supporting my thoughts
Break In Secrets--How To Break In New Motorcycle and Car Engines For More Power
YMMV
