I wasn't aware that the synthetic oils had that much higher of a flash point. Granted you shouldn't need it, but it's a nice insurance policy to have.
Cantilever crank construction only became possible for high specific output engines because of the synthetics. Before that time, it was only used in bronze bearing engines (glow) or low power applications.
I remember the days that oil manufacturers stated 1:50 for their oils (mineral), but everybody kept using the 1:20 mix, especially for >100hp/liter engines. Good mineral base stock oils can easily get away with 1:50 mixes, but they are not cheap either, and certainly are not the run of the mill garden appliance oils like Lawn boy.