What the ??? The viscosity numbers for motor oil, I know this is a shock but what they indicate, is viscosity. ie THICKNESS. A 10W-30 synthetic is exactly as thick as a 10W-30 dino.
A) synthetic is just fine for break in, and B) it's a moot point here because at the time of the 1st oil change your engine is as broken in as it's going to get. If you don't believe me take a look at the Mobil web site, but what would they know about oil?
cheers
mbs