I run premium in all my vehicles and have just started to switch over my quads, mower and small equipment. I do see an increase in fuel economy in my vehicles over regular but I'm running chips on most of them as well so its hard to say if its the fuel or the chips but I run the chips on the performance setting, not the economy.
Whats really driving me me to switch is I've had regular fuel go bad in as little as 3 months. Also I know 2 people that had frozen fuel lines last winter from running regular fuel. Premium has additives in the winter to prevent that.
I have not done a lot of research but have heard that ethanol fuel goes bad faster and doesn't work as well in winter, which is why we have relatively low percentages in our fuel compared to places in the US.