OK - I can't see myself spending over about USD 1500 given that most things have been paid for upfront. At the rate I calculated, that's only about £17, but I obviously don't know how Amex will calculate that.

On my other point re. charge cards - what's the dela if I buy my USD at Thomas Exchange? Will there be a charge if I do it on the Gold card? If so, I'm better off just buying it on my HSBC debit card card.