if you stick to mogas, you'll have synthetic motor oil options for running in your Rotax 912iS and extended hr oil change intervals. Also, less oil consumption.
My oil level seems to sit best at about 1/2 to 2/3 of the range on the stick. Above that, it just seems to disappear in 4 or 5 hours of run time, back to 1/2 to 2/3, where it just sits pretty much constant. Some are going up to 80 to 100 hrs on Mobil 1 motorcycle Racing 4T 10w-40 full synthetic, with gearbox additive, between oil and filter changes.