I travel fairly often and don't always fill up at the same station; But, I've noticed with Conoco and Diamond Shamrock my RS2'd S6 with 370 hp software tends to ping on hard boost.

I threw in a gallon of toulene on a 1/4 tank as a test, the pinging went away. Now I'm trying a tank of Shell and it seems fine. anyone else?

but I'm not RS2'd as of yet. Fortunately in NJ you can buy Sunoco 94 octane at the pump and thats what I always use. If i start getting pinging I'll resort to the toulene :(

When Mihnea was tuning my car, we started out with about a quarter of a tank of Mobile 93. As we worked, Mihnea complained that he was having trouble giving the car timing adavnce. He commented that he had the same problem with Manny's avant and Manny was running the same gas. My friend Carmello piped up from the back seat and said that he had read that Mobile gas has more detergents in it and and that might be a factor. He went directly to Shell at Carmello's recommendation and filled up with 93. Mihnea was able to give me four more degrees of advance.

Since then, I have started using Shell in the Coupe too. Maybe its the cooler weather or wishful thinking, but it feels quicker. Not to bash Mobile, I still run the Mobile 93 in the A6's, and sometimes I run a tank through the Coupe, but the S car seems to make more power on the Shell.

Your findings make sense to me.

After Mihnea tuning, I tried a few gallons (5) of 105 race gas in the car. The difference (if there was one) was not noticeable. The car is tuned to maximize 93.
I have not tried race gas in the Coupe.