I'm in no way up on the fine points of synth vs. dino oil, but one thing I have to ask...
Coming from my old aircooled VW hobby, I dont use synth oil in those engines. This is from a few years back, and things may have changed, but the old VW aircooled engines are picky about heat. Dino oil picks up, and disapates, heat better than synthetic oil, or at least did a few years ago. I'm aware that on the VW end of things this is more critical, due to there being an oil cooler inside the fan shroud, to aide in cooling the engine, and in the XS there is no such beast. My question is, do the XS engines notice an increase in running temps from using synthetic oil over dino oil, or is it a wash due to the XS being more of a true air cooled engine than the VW's air/oil cooled engine?