So I've done some testing with this...
Toptier gas basically has more detergents in it. ( Top Tier Gasoline
In my area at least, I've tested 91 octane gas with DinoCare (toptier rated gas) from a Sinclair station.
When using 91 octane with DinoCare I tend to experience stumbling on cold startups and reduced MPG when compared to 91 octane from the same station without DinoCare.
2014 Mustang GT Premium (deep impact blue)
Too many mods to fit in my sig.
Follow my build list on my blog
. (still updating mods installed so far)