When synthetic oils first came out back in the '60s, the original idea was not to ever have to change it. Just change filters every few thousand miles. The molecules in synthetic oil don't tear apart and wear out like mineral oil. However someone seems to have forgotten the other contaminants that collect is oil that filters have nothing to do with, like water, gasoline, etc.
So, presumably you can run synthetics longer, but the other stuff can still eat away at your engine, so it's not advisable.
You buy synthetic oil because it's marginally better than syn/mineral mixes, but either of them in the motorcycle blend are quite adequate.
Be sure to get a motorcycle blend or some truck oil like Shell Rotella is good. Do not put automobile oil in a bike!
Bare