Just go with whatever the manufacturer recommends. They always have actual data to back up their recommendation. Its not like they have a stake in the gas companies. If that was the case then every manufacturer would only recommend premium.
I've been running e85 not much mpg difference,I'm going to try 91 next tank.E85 was $1.15 per gallon cheaper than unleaded today. I filled up my van on e85 for the first time. I'm down less than 1mpg over 130+ miles so far.
Have you noticed any knocking while using regular? Just asking because premium is recommended for the turbo.I have a turbo .. use regular all the time. Took it on a trip .. kept the speed around speed limit and got close to 34 mpg. Granted it was flat driving with the only hills being the over passes over roads.