Currently I have 548 miles on the Z. Pre 500 miles I have RELIGIOUSLY maintained 4K rpm and below. On highway, I have switched between 5th and 6th gear every 10 minutes (Nissan recommends you to NOT drive in the same RPM for long time during break in). Now that I'm past 500 miles, I am keeping it under 5000 rpm. I think after 800 miles, I'll keep it under 5500 rpm etc. Just increase 500 RPM every 200 miles you drive ... (btw, this is just me. Nissan recommends below 4K all the way to 1200 miles.)
It takes a lot of patience during break in period. Having a 332 HP VQ engine under the hood and not able to rev it above 4K rpm is probably one of the hardest thing you will ever do. But it'll pay off in the long run.
