I use Archoil AR6200 fuel treatment on my stock 964/993. I use it to counteract the harmful effects of ethanol to the fuel system. The advertising claims it combats knocking/pinging and improves gasoline's resistance to pre-ignition. I believe that is what all the competing products claim as well. You will have to decide which one you want to believe. I don't hear any knocking/pinging from the engine during the hot summer drives.
https://www.archoil.com/products/ar6200-fuel-treatment