As an aside (!).. Yet again a thread that highlights two countries divided by a common language...
'Break In Oil' sounds to me like something you'd take with you before engaging in an evening of petty larceny..
Or a 'Plus Gas' substitute, maybe..
For me break-in or running-in a new engine implies a limited use of throttle and load without lugging. The ambient temperature you do your running-in should influence the viscosity index. I use Valvoline 20w-50 VR1 Racing oil for running-in and change it 3 times between initial start-up to 500 miles., then switch to a Comnoz top-of-his-list oil.
I keep wanting to try a straight 30w non-detergent, but don't have enough information and can't afford the emotional consequences if something goes sideways; anyone got any experience with this?