When I rebuilt an engine, the maker of the piston rings that I used called for about 8 to 10 accelerations from 40 to 60 mph at full throttle to get the rings seated to the cylinder walls. Yes, they (Perfect Circle) said full throttle. Part throttle does not force the piston rings against the cylinder walls and the rings do not break in.
Please note, I did not say to rev it to the redline.
Here’s a link to a second opinion from a major aero engine maker. They caution strongly against running the engine at less than 65% full power for the first 50 hrs.
http://www.factoryengines.com/docs/Hard%20Facts%20About%20Engine%20Break-In.pdf