I have read a lot of different articles on break in procedures so I will avoid that one here. But I think the general consensus is that you need to give the mechanical's time to bed in with one another . A good synthetic may in fact not allow that to happen. IMO I would say leave the "break in oil" in it until the first service interval and then make the leap to a good synth!
That is precisely what I did in 1993 and my Cobra is still running smooth as the day it was new thanks (in part) to many quarts of Mobil one!
Changed to Royal Purple 5w20 at 550 miles. No issues.