Both Shell and Costco gasoline are top tier. But at this time, they are clearly not equal on my car's tune.
Not really analyzing our gas options, but I do drive around with the AP connected every once in a while. And you can see how much timing gets pulled during my commute.
You would be the first person I have seen to say that Costco is considered a top tier. Usually that's just BP shell Mobil. Your own research brings into question whether Costco is truly equal to those.