When engines are fully assembled, you know what they do with them before they put them in a car or truck, right? They put them on an engine dynamometer, feed it fuel and take it all the way to the redline (Above what DCX will set the ECU's redline to) before the first mile is put on the engine. They insure the engine meets the SAE-rated power output and that the engine will not grenade itself anytime the customer takes it to the ECM-set redline. In fact there usually is one or two engines that purposely get grenaded, just to see how high and consistently the RPMs can be maintained before utter engine failure. The Pontiac Super Duty 4-cylinder comes to mind, 10,000 RPMs before it grenaded.
As mentioned, utilize the ENTIRE RPM range from 800 to 6,000 RPM. The first 35 miles are critical to engine break-in as this is the only time the roughness on the cylinder walls, used to seat the rings, is available. This is where you determine how you will want to drive the car for the rest of it's life, if gas mileage is your thing, baby it, if performance is your thing, you better be hitting alot of high RPMs during those 35 miles. After 35 miles, up to 1,500 miles, continue using the entire RPM range as often as possible, and plenty of wide open throttle when you can. By doing either you pick your path, low BHP numbers or high BHP.
Don't believe me? I have two Dynojet print-outs, one my former 2003 Mazda6 V6 ATX which was broken in baby-wise and followed the manufacturer's advise on break-in, and then I have one of another 2003 Mazda6 V6 ATX which was broken in hard. Mine dyno'ed in at 159 FWHP, the other made 183 FWHP, both cars bone stock, both pulled in the same gear. I have others from my former Mazda6 forum which prove that breaking it in hard gets you the highest possible BHP numbers.
Unfortunately I got my SXT with 50 miles on it, too many other people test drove and we didn't put any money down to hold it while we shopped around (We test drove it with 6 miles on it). So I am trying to recover what I can of the break-in period.