Just curious, why wouldn't you still be able hit SUBs on your Visa at Costco while others can freely pay with Amex if Costco also accepts that? Why would Amex acceptance at Costco hinder your ability to use Visa? Unless you mean that Costco would only accept either one so your preference is Visa over Amex. But I don't understand why they can't accept all major credit cards like most retailers do, but that's a whole other discussion.