I replaced the rings in an engine myself about a year ago and looked into this quite a bit. What I found was a lot of varied opinions. The advice I settled on was running it hard in short bursts. Essentially, you want to "physically wear the new piston rings into the cylinder wall until a compatible seal between the two is achieved." This take high pressure in the cylinders, which you will not achieve keeping under xxxx rmps, as GM (and every other manufacturer) suggests. What you want to avoid, however, is the cylinder wall glazing over with overheated oil and thereby preventing that interfacing. So you don't want to run it hard for long periods.
So if it were my new car, I would nail it on the on ramps, but I wouldn't do laps at the track in the first ~500 miles. A manufacturer will never tell you to run it hard, of course, for liability reasons.
More detailed information:
New Engine Break-in Procedure
More fun reading:
Break In Secrets--How To Break In New Motorcycle and Car Engines For More Power
My opinion for what it's worth is this method. Drive it like you stole it the first few hundred miles with the right oil. Syn. thereafter.Check out the C7 oil ingestion thread by tuner boost. Makes lots of sense to me. Here it is . Enjoy the articles and your machine!
What happens now days is these engines come prefilled with M1 full synthetic, a superior oil that provides excellent protection from friction, etc. This is great for an engine that is already broken in and rings have seated properly, but it also makes the ring seating to begin with a crap shoot (GM still has excess oil consumption as the #1 warranty related service visit) as this initial period from new the rings and cylinder walls need to "wear in" to each other for a good seal. After 400-500 miles a very hard glaze sets in and then there can no longer be any further seating (we seat rings and break-in our race motors 2 runs down the track, street engines the first 100-200 miles, and rarely ever have anything but the best ring seating one could hope for).
Here is what happens when an engine is not run hard enough to create enough load on the rings to overcome the lubrication provided by the oil used:
In the old days, and still today with aviation engines that the pilots life depends on it, break in oil (a conventional mineral based) came pre-filled and it provided enough protection for the bearings and journals IF driven easy the first 500-1000 mile, yet allowed enough friction for the cross hatch hone to seat the rings properly. It was then critical to drain and fill with a good oil and then could be driven hard. If you went from the showroom to the race track with break-in oil back then you stood a good chance of spinning a bearing or worse.
Today, marketing has conditioned the buyer to get in the new car and aside from put gas in, never open the hood or consider doing any maintenance until 10k or so miles when a DIC message prompts them to do so, so this has resulted in all the re-ring jobs since 1997 when the LS1 was first introduced (that and the piston slap that was addressed with coated skirts) and GM to this day takes the stance that "consumption of 1 qt of oil per 1500 miles is considered normal" when there is no way this should occur.
So, aside from immediately draining the syn oil before driving your new car and filling with conventional to aid ring seat, driving it hard (not unsafe, not abusing it) for several full throttle accelerations, and deceleration (rings need to be loaded with both for proper BMPE to seat properly) one can then drain and change oil/filter to remove break-in debris and be confidant that the rings have seated properly and oil consumption at a minimum, and power at a maximum. The heat cycling process is also critical, during this first 50 miles stop a few times and let the engine cool and then continue.
Now we recommend driving easy the first 50 miles so the ring and pinon mesh properly and the brake pads bed as well, but other than that, there is no real critical drivetrain parts needing any break-in.
Here are some links to back this up for the skeptics (remember, the engineers don't write the owners manual):
This one probably the most informative and detailed:
http://www.tcmlink.com/visitors/carenfeed/brkin.pdf
Proper Engine Break-In - AVweb Features Article
Break In Secrets--How To Break In New Motorcycle and Car Engines For More Power
New Engine Break-in Procedure