According to the latest Issue of American Iron Magazine you should Not use Synthetic Oil when Breaking in a New Engine.
Don't know who wrote that article, but he's full of (it)...and so is AI for publishing the article. Talking only about the oil, not all the additives (friction modifiers, viscosity modifiers, anti-wear additives, pH buffers, etc.):
The only difference between natural and synthetic oil is that synthetic stands up to higher temperatures than natural. That's all it is. So synthetic is a much better choice for our air/oil cooled bikes.
What separates high quality motor oils from the others is the use of a high quality full-synthetic base oil with a high quality additive package.
95% of the auto/motorcycle/atv/you-name-it magazines are nothing but a mouthpiece for their advertisers. Ever notice there's a tech article for Brand X mufflers, and within a few pages there's an ad for the same Brand X cans? That's not a coincidence.