RE: breaking in a new motor
I prefer a super controlled environment for break in. Only an extreme few have that available. They might have a bench but they never, ever, have a suitable and adjustable cooling air supply. So that leaves them with an aerial break in, which when done reasonably well does a great job. A poorly executed bench break in can and does do more damage than good. A badly done aerial break in leaves one with the same results as a bad bench break in. Bad ring seals, low compression, lower than normal RPM, and a scored cylinder wall. It all comes down to self restraint, and a little understanding of what needs to be done for the best long term performance.
What must be understood is that numerous engines may need to be subjected to the break in process at the same time, so those have to be bench run to get the job done. If you have 10 or 20 engines that have to be broken in and tuned for shipment on the same day, and that process will be repeated over numerous days, the bench is the only way it can get done because you can do many at the same time if you are set up for it.