I've worked on too many engines to count, but what I do know is the owners that had engines with cleaner cylinder heads valves and piston rings usually used premium or middle grade at the least (and usually had proper oil changes also) . Also valve recession was less (also contributed to heat). If you would like to do a test do this-check your valve lash, write the clearance/dimension down in a log book. Use premium for (1) year and record the valve lash dimensions at each service. Assuming you ride approx the same miles/per year, Then use the regular grade for a year and do the same valve lash recording, pull the carb float bowl off every other service and look inside it. Use the same brand motor oil and correct service intervals. I've had several of my own engines/bikes/scooters that I have over 50k miles and had only had to make (1) or (2) adjustments ! I use synthetic oil and premium gas because I've learned from others (and many years experiance). I don't work for an oil company, but I do have to work, and if spending a little more at the pump and at oil changes to make my motors last longer, I don't have to work on them as much.